Life of Robert Stephenson by William Pole: Chapter XIV

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CHAPTER XIV. The Atmospheric System of Railway Propulsion

THE attempt that was made some years ago to introduce the atmospheric system of propulsion upon railways, forms such a remarkable episode in their history, that it deserves a somewhat extended notice.

The invention here referred to is often termed the ‘ Atmospheric Railway,’ but this is a misnomer. In the economy of railways, whether scientifically or practically considered, it is always desirable to distinguish between what relates to the road itself, and what has more especially to do with the movement of the vehicles upon it. The design and construction of the road are matters quite distinct from the system of haulage used; and the atmospheric plan, being simply a peculiar mode of producing locomotion, forms no essential part of the railway properly so called.

It is proposed to give in this chapter a short historical and descriptive notice of the Atmospheric System of Railway Propulsion, from its invention, through its season of popularity, to its ultimate abandonment; and we shall dwell particularly on the part taken in its history by Robert Stephenson. He was from first to last its determined and consistent opponent; at one time almost standing alone, in the face not only of the promising appearance of the invention, but of the conscientious and powerful advocacy which it received from many of his most eminent brethren in the profession.

There are three modes by which locomotion is usually effected upon railways; namely, by animal draught, by locomotive steam engines, and by stationary steam power.

The first was given up at a very early period, as inadequate to the requirements of railway traffic, and is now only used in exceptional cases ; but between the second and third, i.e. the locomotive engine and the various modes of applying stationary steam power, to which latter class the atmospheric system belongs, there has been an almost constant rivalry.

At the time when the Liverpool and Manchester Railway was formed, both systems had been tried. George Stephenson had introduced his locomotives on the Stockton and Darlington and other lines; while the plan of drawing the carriages along by stationary engines and ropes had also been used extensively by him, and was at work in many parts of the country. When the railway approached completion in 1828, the directors, having determined that some more efficient power than horses must be used, consulted two eminent engineers, Mr. Walker and Mr. Rastrick, as to which application of steam power, the locomotive or stationary, would be preferable for the purposes of line.

These gentlemen, after studying the examples of two systems then in existence, gave their opinion that, if it were resolved to make the railway complete at once, so as to accommodate the full traffic expected, the stationary system was best;— but that if any circumstances should induce the directors to proceed by degrees, and to proportion the power of conveyance to the demand, then locomotive engines would be preferable. In any case, however, they considered it necessary that stationary engines should be used on the two inclines at Rainhill and Sutton, with gradients of one in ninety-six, to which they considered the locomotive system inapplicable.

In reviewing the detailed facts and reasonings given in the reports, it would appear that the principal, if not indeed the only ground for the preference of the stationary system was a saving of something over twenty per cent, in the cost of working, maintenance, and interest of capital, which the referees considered would accrue by its use. Other points of comparison are mentioned, but no very decided opinion appears to be expressed in favour of either plan, except for the reason above stated.

The referees, therefore, evidently laid themselves open to attack on their main ground - namely, their estimates - from any one who had sufficient knowledge of the working of the two systems to detect any errors into which they might have fallen; and the cudgels were soon taken up by George Stephenson in defence of the locomotive. He urged strongly its superiority, in numerous reports and at numerous meetings of the directors, until at length this body, influenced by his persistent earnestness and by the undeniable weight of his arguments, resolved to adopt it, and instituted a public competition to determine the best form of the machine, the result of which is well known.

An excellent resume of the arguments used, on these occasions, by the great founder of the locomotive system is given in a tract published in 1830, under the joint authorship of ‘Robert Stephenson and Joseph Locke, civil engineers.’ Robert lent his father very active aid in this matter; and it is clear that he had, at this early stage of the controversy, thoroughly mastered the principles of the dispute, and acquired the strong convictions in favour of locomotive power which he afterwards so unflinchingly adhered to.

The joint essay attacks, with much force, the correctness of the estimates of the referees, asserting that, instead of the stationary system being the cheaper in the working, there would be an economy in favour of the locomotive in the proportion of eight to five. It points out that the capabilities and advantages of the locomotive system had not been properly appreciated, and that some disadvantages of the rival plan had been overlooked ; and it concludes with some able and far-sighted remarks on the two systems generally, which, as bearing strongly on the subsequent revival of the stationary plan in the atmospheric form, it may be useful to reproduce here.

In drawing a comparison (say the authors) between locomotive and stationary engines, the relative expense is certainly of vast importance; but, though this is a primary object, that of despatch and public accommodation is of the utmost consequence, and may be said to rank higher in the scale of importance than expense, when the difference between the two systems in the latter item is not very great. When the traffic upon a railway is either small or variable, the locomotive engines are not only cheaper, but much more convenient, because the number of engines in operation at one time may be regulated as the trade fluctuates ; but when the stationary system is adopted, the whole of the machinery must be employed to convey the goods, however trifling. Where the trade is great and nearly uniform, as is the case between Liverpool and Manchester, the expense of the stationary system approximates probably more nearly to that of the locomotive than in any other locality in England. It is in this instance, therefore, that despatch and public accommodation claim particular attention.

In this respect Mr. Walker is of opinion that either system is fully adequate; but he does not appear to have duly considered the practical difficulties which are unavoidable where a chain of stationary engines is employed. Locomotive engines may be compared to horses, as far as convenience is concerned, with this advantage, that they are much more manageable, because each engine is an independent power; but the case is widely different in the other system, where the whole is dependent on each individual part, and also on a series of regulations liable to be deranged by the inattention of workmen. With the locomotive engines the carelessness of one person extends in most cases only to one train of carriages, whereas an accident produced by the same cause with stationary engines occasions a delay from one end of the road to the other, and the risk of accident is evidently proportionate to the length of the line of road. We may go so far as to conceive a line of railway with stationary engines so long that accidents would be almost perpetually occurring, which leads to the inference that the conveyance of a large quantity of goods by such a series of engines and ropes would, in the end, become actually impracticable.

From the local situation of the Liverpool and Manchester Railway, it is evident that in a very few years several branches from the various towns on each side will join the main line. Hence the traffic on the different parts of the line will annually undergo some modification. If, however, the stationary system were established in the outset, it would be necessary to construct the engines of sufficient power to meet any probable increase of the kind, and much difficulty would arise in adjusting the power of the engines requisite for the different parts of the line of road, excepting, indeed, they were all made very powerful to meet any future increase of trade. These and other difficulties, which are inseparable from the stationary system on a public line of road, where the trade must necessarily fluctuate, are easily and effectually obviated with locomotive engines; for should the trade in any part undergo a temporary increase, or decrease, the requisite power may be immediately applied, or withdrawn.

Many other practical considerations might be adduced to exemplify the great superiority of the locomotive over the stationary system on a public railway, but they are of a description not easily understood or duly appreciated, except by those who have had experience and frequent opportunity of witnessing the daily operation of machinery on railways. Obstacles often arise from casualties, which by bare mention in this place would appear frivolous ; whereas to the practical man they are of importance, and tend to demonstrate that it is of great consequence to adopt a system, the efficient operation of which, as a whole, is not dependent on each individual part.

The result of the locomotive competition on the Liverpool and Manchester Railway gave such a strong confirmation to the decision of the directors, by exhibiting the great power of the locomotive, that it appears to have put the rival system out of sight for some years; but the idea of stationary power was too plausible not to be revived. The broad fact was obvious enough, that to convey an engine and its boiler through the air, at a speed of twenty or thirty miles an hour, exposed to all weathers, and to all accidents of a precarious road, and consuming a large portion of its energy in moving its own weight along, was not the most advantageous way of applying steam-power. It was not wonderful, therefore, that any plan should be received with favour, which offered an apparently feasible application, to railway haulage, of the power of an engine, safely housed with its various appurtenances in a fixed building, where it could be worked in the most advantageous way.

The invention of the atmospheric plan of propulsion offered this promise. It was assumed that the principal fault of the stationary system, as hitherto applied, lay in the rope, as a means of transferring the power from the fixed engine to the moving train; and undoubtedly, by its great friction and liability to accident, the rope was a serious evil. The principle of the atmospheric invention consisted simply in substituting for the rope another means of transmitting the power, which was conceived to be much superior, and the introduction of which, it was thought, would entirely remove the objections to the stationary system, and leave its admitted advantages available, without the drawbacks that had formerly interfered with its application.

The first idea of transmitting power to a distance by means of pneumatic pressure appears to belong to the celebrated Denys Papin, who described, in 1688, an apparatus, in which a partial vacuum, produced in a long tube by air-pumps fixed at one end, caused the motion of pistons placed at the other end. Mr. Farey, a well-known mechanical authority, writing of this scheme of Papin’s in 1827, says: ‘ It is rather surprising that so simple and advantageous a method of exerting power at a distance from the first mover, should have remained neglected and unnoticed so long as it has been.’

But the more proximate inventor of the system of which we are now treating, was a London mechanical engineer named George Medhurst, who, long before railways were thought of as a general means of conveyance, proposed and described a plan of locomotion by atmospheric pressure, precisely similar in principle to that afterwards used.

His first notions on the subject were published in 1810, when he described his invention of ‘New machinery for the rapid conveyance of letters, goods, and passengers by air.’ He proposed to enclose letters and papers in a fight hollow vessel, so formed as to fill the area of a tube, and to move freely through it; when, by forcing air into one end of the tube, he assumed that he would be able to drive the vessel through the tube at a great velocity. He further proposed to extend the principle by making the tube large enough for a four-wheeled carriage to run inside it, on an iron road, carrying goods and passengers through the kind of tunnel so formed.

In 1812 he again published a notice of his scheme, but adding the important conception that the necessity of putting the passengers and goods within the tube might be avoided, by substituting a much smaller pipe, the piston of which should communicate ‘by a particular contrivance through the side of the tube ’ with the carriage outside, and so drag it along. The nature of this - particular contrivance ’ he did not, however, disclose till 1827, when, in a third pamphlet, he described various modes of effecting this object. The mode with which we have to do here, introduced, on the top of the tube, a kind of longitudinal flap, riveted along one side, but loose on the other. The piston, running within the tube, had a wheel in front, which, as it passed along, lifted up the flap, forming a slit sufficient to allow a bent rod to pass through from the piston on the inside to the carriage on the outside, so as to give motion to the latter as the former was propelled by the pressure of the air. When the piston had passed, the flap closed of itself, the loose edge falling against a face of leather, or some other soft yielding substance, which made a joint sufficiently tight to prevent leakage under the small pressure the inventor proposed to employ.

Another important step in Medhurst’s scheme of 1827 was that he proposed to work his piston both ways - one way by forcing air into the tube behind the piston, or by what may be called the plenum impulse;— the other way by exhausting the air before the piston, or by the vacuum impulse. Taking this latter modification we have the perfect anticipation, as far as the idea is concerned, of the atmospheric system subsequently introduced upon railways. The merit of later inventions consisted in the perfection of the details of the apparatus, which Medhurst does not seem to have considered with much care. His invention was probably far too much in advance of the then notions of locomotion to meet with any encouragement for its actual trial.

It is right to mention that the first publication of any proposal for locomotion by Papin’s vacuum principle appears to have been by a Mr. John Vallance of Brighton, who, in 1824, re-proposed Medhurst’s plan of a gigantic tube, substituting, however, the vacuum for the plenum mode of action.

An agitation was got up at Brighton a year or two later for the trial of Variance’s plan between that town and London. A short trial-tube of the full size was constructed and worked by way of experiment; and it is well remembered how, for want of due precaution in checking the impetus of the carriage, the venturesome experimental passengers were occasionally blown out of the end of the pipe into a field beyond. But this attempt only had the result of furnishing jokes for the pantomimes of the day, and of producing a rather acrimonious paper war between the supporters and the opponents of the scheme. Mr. Vallance does not seem to have known or thought of the much more feasible plan of smaller tubes.

In 1834 Mr. Henry Pinkus, an American engineer, proposed a modified contrivance for opening and closing a slit at the top of the tube, by means of a flexible valvular cord. This was patented in the same year, as also were other modifications for the same object in 1835 ; but the proposition appears to have had no practical result, and Medhurst’s ideas remained in abeyance until a few years afterwards, when Mr. Samuel Clegg, an engineer well-known for the important part he took in the introduction of gas-lighting, turned his attention to the subject. After studying it well, he adopted Medhurst’s general arrangement of a vacuum tube, with a longitudinal slit in its top, but he contrived a form of valve for closing the aperture much superior to any that had preceded it. This was patented by Mr. Clegg, January 3, 1839, and a tract giving an account of the whole system of locomotion thus arranged, and calling attention to its advantages, was published in the same year.

But Mr. Clegg did not work alone in the matter, for, before the date of his patent, he had associated himself with an engineering firm— Messrs. Jacob and Joseph d'Aguilar Samuda, eminent manufacturing engineers of Southwark— who, apparently impressed with the value of the invention, lent it powerful aid, not only by their mechanical and engineering skill, but by the energy with which they advocated its advantages. Messrs. Samuda, in 1844, obtained a supplementary patent for improvements, and through all the experiments and discussions which took place on the subject they were the most active and prominent supporters of the plan.

Soon after the date of the patent, Messrs. Clegg and Samuda laid down at their own premises and elsewhere small model tubes, which answered their expectations; but, not being satisfied with private experiments, they endeavoured to get the system tried actually upon a railway, and accordingly obtained permission down, at their own expense, an experimental upon a short line at Wormwood Scrubs, which had been made to connect the London and Birmingham and the Great Western Railways with the Kensington Canal, and which, though only a mile or two in length, was dignified with the name of the ‘ Birmingham, Bristol, and Thames Junction Railway.’ A vacuum pipe, half a mile long and nine inches internal diameter, was laid down on the part of the line between the Great Western Railway and the Uxbridge Load, where the gradient was about 1 in 115, and where therefore the efficiency of the power in ascending inclines was put to the test.

This was set to work in June 1840; and as it was a complete exemplification, on a real scale, of the proposed plan of atmospheric propulsion, it may be as well to insert in this place, once for all, the description of the apparatus as given by the inventors.

The accompanying figures will serve to illustrate the description. (See PDF version for the drawings)

Fig. 1 is a general side view of the front part of the train and the atmospheric tube, the latter being delineated partly in longitudinal section to show the piston, and its attachment to the leading carriage. Fig. 2 is a transverse section of the same parts. Figs. 3, 4, and 5 are transverse sections of the tube only, enlarged to show the details more clearly, and to explain the action of the valve. In fig. 3 the valve is shown open, the piston passing through; fig. 4 shows the method of closing the valve and sealing the composition; and Fig. 5 represents the valve as finally left after the carriage has passed by.

The same letters refer to the same parts in all the figures.

The moving power is communicated to the train by means of a continuous pipe or main A, laid between the rails, and divided by separating valves into suitable and convenient lengths for exhaustion. A partial vacuum is formed in each length of pipe by steam engines and air pumps fixed at intervals along the road. The separating valves are opened by the train as it advances, without stoppage or reduction of speed. A piston B, which is made to fit air-tight by a leather packing surrounded by tallow is introduced into the main pipe and connected to the leading carriage of the train by an iron plate c, which travels through a longitudinal opening made along the top of the pipe for its whole length. This opening is covered by a valve G, extending also the whole length, formed of a strip of leather riveted between iron plates; the top plates are wider than the groove, and serve to prevent the external air from forcing the leather into the pipe when the vacuum is formed; the lower plates fit the groove when the valve is shut, as shown in Figs. 4 and 6, and, by making up the circle of the pipe, prevent the air passing the piston. One edge of this valve is securely held down by iron bars a a fastened by screw bolts bb to a longitudinal rib c, cast on the pipe on one side of the opening; and the leather between the plates and the bar, being flexible, forms a hinge as in a common pump valve; the other edge of the valve falls on the surface of the pipe on the opposite side of the opening, thus forming one side of a trough F, as shown in Figs. 4 and 5, This trough is filled with a composition of bees’-wax and tallow, which is solid at ordinary temperatures, but softens when slightly heated. The composition, when so heated and pressed down, adheres to the edge of the valve, which forms one side of the trough, and to that part of the pipe which forms the other, and so makes an air-tight junction between them.

Supposing now the air to be exhausted from the part of the tube in front of the piston; the atmosphere having free access to the part behind it, will press upon it with a force proportional to its area and the degree of exhaustion ; and the effect of this pressure will be to propel the piston along the tube, dragging with it the leading carriage to which it is attached, and the train coupled behind.

As the piston advances, the valve G must be raised to allow the connecting plate c to pass, and this is effected by four wheels H H H H, fixed to the piston rod behind the piston: the aperture thus formed serves also for the free admission of air to press on the back of the piston. When the wheels have passed by, the valve falls again by its own weight.

But by the operation of raising the valve out of the trough, the composition between it and the main pipe has been broken, and the air-tight contact must be reproduced. To effect this, another wheel K (Fig. 4) is attached to the carriage, which serves to ensure the perfect closing of the valve by running over the top plates immediately after the piston rod has passed ; and a copper tube or heater N, about five feet long, filled with burning charcoal, is also fixed to the under side of the carriage, and passes over the surface of the composition, softening it and pressing it down, so that when on cooling it becomes solid, it seals the joint air-tight before. Thus each train, in passing, leaves the pipe a fit state to receive the next train.

A protecting flap or cover i, formed of thin plates iron about five feet long, hinged with leather, is made to he over the valve, to preserve it from snow or rain; the end of each plate underlaps the next in the direction of the piston’s motion, being lifted up by wheels D (Fig. 3), fixed under the advancing carriage, and allowed to close again as it retires.

The parts above described constitute the essence of the plan. Much ingenuity and care were bestowed on the arrangement of other details, such as the entrance, exit, and separating valves, the mode of effecting junctions and crossings, the construction of the tube, the manner of connecting together the pipes of which it was formed, the arrangement of the exhausting pumps, &c. &c. But it is not necessary here to go into these particulars.

The exhausting pumps on the experimental line Wormwood Scrubs were worked by a steam engine fifteen horse-power, and produced in one minute vacuum in the pipe equal to about 18 or 20 inches mercury; and by maintaining this exhaustion, it was found that, even with the small pipe used, a load of 13.5 tons could be propelled up the incline at a rate of 20 miles an hour; or with a vacuum of 23.5 inches, a load of 5 tons would go 45 miles an hour.

These trials were considered so successful, and seemed to promise so much for the new system of propulsion, that they naturally attracted the attention of persons interested in railways, and among these was Mr. James Pim, treasurer of the railway between Dublin and Kingstown, who, after having carefully observed the experiments, became a most energetic advocate of the plan. It appears that the railway with which he was connected, had a short piece of line from Kingstown to Dalkey, which had been used for the transport of stone for the new works at Kingstown Harbour, and which, having steep gradients and sharp curves, offered what were then considered rather formidable difficulties to the working of the line.

About May 1841, Mr. Pim wrote a letter to Lord Morpeth, asking the permission of the Board of Public Works of Ireland (under whose care the Kingstown and Dalkey road was placed) for the parties interested in the experiment to lay down an atmospheric apparatus along this line.

It appears, however, that the sanction of the Board of Trade was needed to carry out this proposal, and Mr. Pim, nothing daunted, wrote towards the end of the same year a letter to the Earl of Ripon, President of the Board, describing clearly the principle and mode of working of the atmospheric system, and giving a lucid and forcible statement of the arguments in its favour; the object of the letter being to ask the Board to refer it to such persons as their Lordships might select, to enquire into the several statements made, and in their report to state particularly whether the invention was entitled to a further and more extended trial.

The request was granted, and two scientific referees— Lieut. Col. Sir Frederic Smith, E.E., E.E.S., and Professor Barlow, F.E.S. were accordingly appointed to investigate the merits of the plan.

Their report was dated February 15, 1842. It appears that they conducted experiments, in January, on the model fine at Wormwood Scrubs, which generally corroborated those of the projectors; and after making the necessary calculations and deductions, they reported that they considered the principle of atmospheric propulsion to be established; that its economy of working would increase with the scale on which it was applied; and that it appeared well suited for such a fine as that from Kingstown to Dalkey. On the points of first outlay, cost of working, safety, and convenience, as compared with the locomotive system, the referees did not venture any very decided opinion.

The report was, however, sufficiently favourable to warrant the Government in sanctioning the trial of the principle on the Kingstown and Dalkey fine, and in granting a loan of £25,000 to the Company for the purpose. This determination was due to the influence of the late Sir Robert Peel, then First Lord of the Treasury, who was on this occasion, as well as during its whole history, a strong supporter of the plan.

With this encouragement, the railway was accordingly prepared, the tubes laid down, the engines erected, and the apparatus was set to work in August 1843.

The line was single, and about one mile and three-quarters in length. It had a short descent from Kingstown, after which it rose to Dalkey with an average gradient of about 1 in 116 ; the steepest part, 1 in 57.5. There was one considerable curve, of 518 feet radius; a shorter one of 570 feet radius ; and a third, of 700 feet radius. The atmospheric tube was 15 inches internal diameter, placed in the middle of the road, between the two rails, and firmly attached to the cross transoms under the sleepers. It was in lengths of 9 feet each connected by socket joints carefully filled with cement. The width of the longitudinal valve opening was two and a half inches. The arrangements of the valve were made with all possible care, and with the benefit of all the experience gained by the previous experiment.

The pipe did not extend the whole length of the road, but stopped short of the summit of the hill by 560 yards, the carriages running up this distance by their momentum alone.

The steam engine was placed, for the sake of convenience, at about 500 yards from the upper end of the tube, being joined to it by a connecting pipe of equal diameter. The engine was of 100 horse-power, working an air pump of 67 inches diameter, with a stroke of 5 feet 6 inches.

Experiments made on the line, soon after the opening gave good results as to the action of the apparatus. It was found that a rarefaction of 13 to 14 inches could be obtained in two minutes, and 22 inches in five minutes; the pump making 22 strokes per minute. And in running trains up the incline, it was observed that 30 tons could be drawn up at a speed of about 30 miles an hour, and 70 tons at about 20 miles; which, considering the difficulties of the road, was certainly satisfactory.

This confirmation of the results previously obtained on a smaller scale served to increase the popularity of the new invention, and to stimulate its promoters to urge its claims upon the railway world, with a view to securing its more extended adoption.

It may be well here to give a summary of the chief arguments which, at various periods, were urged in favour of the atmospheric system, as compared with other modes of railway locomotion.

The more cogent of these took the shape of objections to the locomotive engine. It was said—

(1) In the first place, that to make a steam engine locomotive was eminently unfavourable for its economy of fuel; that the quantity consumed was excessive, and the kind expensive.

(2) That this was also a very unfavourable condition for keeping the engine in repair, and that the necessity of having a large stock of engines constantly under examination in ‘ hospital ’ led to a very large extra outlay of capital.

(3) That the locomotive engine had to overcome the friction and other resistances due to itself, and to the tender carrying its supplies of fuel and water; to which had also to be added a resistance peculiar to this machine, that of the back pressure on the pistons caused by the blast-pipe.

(4) That in addition to this loss, it had also, in ascending gradients, to overcome the gravity of itself and its tender.

(5) That the use of the locomotive involved many other minor evils—such as the necessity for repairing shops and running sheds, distributed over the line; the liability to slipping on the rails, to fire, to bursting, to freezing of the pumps, and to many accidental causes of derangement and mischief which did not exist with stationary power.

Such were the principal evils said to be inherent in the locomotive system. The only form of stationary power with which the atmospheric plan could be compared, was that of the rope, and to this it was objected —

(6) That the friction of the rope was enormous, and that in ascending inclines the weight of the rope was also the source of much loss of power.

The advantages peculiar to the atmospheric system were stated to be:—

(7) That it got rid of all the disadvantages named in the first five heads, as inherent in the travelling form of the motive machine, and was free also from the objections to the use of a rope with stationary power, as the air in the tube did the duty of the rope without either weight or material friction.

(8) That it presented much greater safety than the locomotive plan, for several reasons,— that it was quite impossible any two trains could come into collision, either by meeting or overtaking each other; that the leading carriages could not get off the rails ; and that all the manifold elements of danger inherent in the locomotive were avoided.

(9) That any desired speed of travelling might be obtained, by simply proportioning the engine, pumps, and pipe accordingly, without corresponding disadvantage in the application of the power. And that, therefore, higher speeds might be attained on railways generally.

(10) That as a consequence of the more favourable application of the power, and the less danger of getting off the line, much steeper gradients and sharper curves might be used, than on lines prepared for locomotive haulage ; and that consequently the cost of constructing railways might be-very much lessened; the economy being further enhanced by the reduced height of all tunnels and over-bridges, consequent on the absence of the locomotive chimney—and the less strength required for viaducts and under bridges, which would have less weight to carry.

(11) That a further and still greater saving in first cost would result from the fact, that the principle of atmospheric propulsion, by ensuring regularity in the working of the trains, would admit of a single line being used, with safety, for an amount of traffic which on the locomotive system must imperatively demand a double line.

(12) That by doing away with the heavy locomotive, much might also be saved in the first cost and in the maintenance of the permanent way; as fighter rails might be used, and they would be much less liable to deterioration and derangement.

(13) It was further contended that the atmospheric system offered much more convenience to the public, inasmuch as it would be the interest of the companies, under this system, to despatch light trains very frequently ; whereas the use of locomotive power rendered it advantageous to reduce their number, and concentrate their weight, as much as possible. And it was also added that the atmospheric system was much more agreeable to the passengers, for several reasons, such as the entire absence of dust and sparks from the engine, less noise, more steady and comfortable motion, better condition of the road, &c. &c.

(14) And finally, it was said that the atmospheric system would enable water power to be used, where it existed, instead of steam; and that, where a sufficient quantity and fall could be obtained to produce a vacuum, machinery might be dispensed with altogether.

The popular and plausible nature of many of these arguments could not fail to attract the attention of the public; particularly as the new plan proposed was no mere untried scheme; for it was in actual practical application, working the traffic daily over a line which, for locomotives, at that time, had been admitted to be almost impracticable.

It was no wonder, then, that the atmospheric system, working on the Kingstown and Dalkey fine, at the end of the year 1843, should be carefully examined by railway engineers ; and among the first to give attention to it was Robert Stephenson.

About this time an application was made to the Directors of the Chester and Holyhead Railway, (who were then promoting their Bill in Parliament,) with a view to the application of the system on that line. The directors, feeling that an investigation ought to be made, commissioned Mr. Stephenson, their engineer, to examine the invention, and to report to them whether he could recommend its application to their railway. He undertook two series of careful investigations, and his report to the directors thereon was dated April 9, 1844, only a few months after the opening of the Dalkey line ; so that Mr. Stephenson appears to have been the first independent investigator of the system, in its application on a practical scale. The results of this scrutiny are so important, when taken in connection with what afterwards occurred, that it is necessary to give them at some length.

Mr. Stephenson commences his report by a passage which well illustrates the importance he attached to the investigation. He says to the Directors :—

When I first visited Kingstown at your request, I made such experiments as appeared sufficient to enable me to form an accurate opinion on the application of this new motive power to public railways. On my return to England, however, I found, by analysing the experiments, that many of the results were irreconcilable with each other, presenting anomalies in themselves, and suggesting further enquiry.

It was then that I began to feel the onerous and difficult nature of the task I had undertaken. I was called upon, in short, to decide Whether a singularly ingenious and highly meritorious invention was, or was not, to be applied to the Chester and Holyhead Railway. I also felt strongly that whatever might be my opinion, whether favourable or unfavourable, the final destiny of the invention was not in my hands; and that if it were really calculated to produce the remarkable results which had been stated, nothing could stop its universal application to railways. On the other hand I saw that, if the principles of the invention were not soundly based, I should be incurring a most serious responsibility in recommending its application to the Chester and Holyhead Railway, extending over a distance of eighty-five miles.

Under this conviction, I arranged an entirely new and extended series of experiments, with the view of fully and accurately testing every part of the invention, and thus putting myself in a position to give you an opinion upon which I could recommend you to act.

Mr. Stephenson further paid a deserved compliment to the engineers who had introduced the system, by stating that ‘ the mechanical details of the apparatus employed at Kingstown had been brought to a remarkable degree of perfection.’

In commencing his investigations Mr. Stephenson first took means to test the actual capabilities of the apparatus, irrespective of any hypothesis, by ascertaining the maximum velocity attainable with trains of various weights, noting also the corresponding pressures in the vacuum tube; and an elaborate statement is given of 20 experiments of trains actually conveyed up the inchne, gradually increasing in weight from 23.25 to 64.75 tons. The general results may be thus stated.

With the lightest trains, of 23 to 25 tons, a velocity of 30 to 35 miles an hour was attained, with a vacuum of 13 to 17 inches of mercury.

With medium trains of 40 to 45 tons, a velocity of about 25 miles an hour was arrived at, with 22 inches of vacuum.

With the heaviest trains of 60 to 65 tons, a speed of 16 to 18 miles an hour was attained, with a vacuum of 23.5 to 24.5 inches.

Mr. Stephenson proceeded to reason upon these actual facts exhibited. He showed that, supposing the apparatus to be in every respect perfect, the velocity of the piston in the tube, when uniform motion was attained, would be, to that of the air-pump piston, inversely as their areas; but that, from various imperfections inherent in the system, this was not practically the case.

The nature and influence of these imperfections therefore formed the next subject of investigation, and the principal of these was the leakage of air in consequence of various defects in the joints, but principally through the longitudinal valve at the top of the tube. He tried a series of experiments to determine this, and came to the conclusion that whatever might be the degree of rarefaction of the tube, nearly equal volumes of air, measured at atmospheric pressure, would leak into the tube in equal times; this curious result being apparently due to the fact that at high pressure (when greater quantities might have been expected to enter) the valve was forced closer, and the apertures of leakage were reduced in proportion. The average amount of leakage, measured at atmospheric pressure, he found to be 186 cubic feet per minute per mile of tube, or 252 feet for the whole length, to which had to be added 219 cubic feet per minute for the connecting pipe and air pump.

But Mr. Stephenson went on to show that, although the atmospheric volume leaking in was pretty uniform at all pressures, the effect of this, as regarded the power required to remove it from the tube, was extremely variable under different degrees of rarefaction; for since the entering air would become expanded according to the rarefaction, and since the air pump could only extract a fixed volume of the rarefied air at each stroke, the power and time required to overcome the effect of the leakage must increase very rapidly with the degree of exhaustion used. And hence, as the exhaustion advanced, the retarding influence of the leakage on the speed became more and more serious, and the maximum velocity attainable by the train proportionably lowered.

Having determined the value and effect of the leakage, Mr. Stephenson calculated what velocity the Dalkey tube ought to give, at the assumed ordinary speed of the air pump — first, supposing the apparatus to be perfect, and secondly, allowing for the effect of the leakage; the difference between which was found, with a vacuum of 18 inches, to be 13 per cent, and with 24.5 inches to be 30 per cent, this difference expressing the calculated loss due to the leakage.

These calculations were then further tested by actual results of experiments with the trains, which showed that the real velocity attained fell still short of this latter result by quantities varying from 26 to 41 per cent, giving the total departure from the theoretical state of perfection 39 to 71 per cent.

The causes of this latter or additional loss of effect Mr. Stephenson attributed partly to further imperfections in the air pump, when in motion, beyond those observable when at rest; and partly to the leakage round the propelling piston, which he considered was much augmented during its swift motion in the tube.

Next followed a series of calculations on the power consumed in giving motion to the trains, under the various circumstances. These calculations were exceedingly elaborate, and, from the evident desire of Mr. Stephenson to present to his readers all the data which had led him to his conclusions, were made somewhat complicated and abstruse as well as lengthy. He had indicator diagrams taken from the air pump at various states of the rarefaction (which are published in full in, and by this means - taking, as before, the assumed speed of the air pump - he arrived at the power expended by the steam engines to produce the results obtained, some idea of which may be formed from the following statement'

With a train of 26.5 tons, which attained a uniform velocity of 34.7 miles per hour, the total power expended was 322 horses.

With 45.5 tons, attaining 25.2 miles an hour, the power was 427 horses.

With 64.7 tons, at 16.7 miles an hour, it was 415 horses.

These amounts, however, included the power expended to raise the vacuum, and to start the train, which was generally more than what was necessary to keep it in uniform motion. The value of the latter came out practically at a pretty nearly uniform value of about 170 to 180 horses’ power for all trains and speeds, and all degrees of exhaustion.

It was next calculated what portion of this was actually applied, through the tube piston, to the propulsion of the trains, which was found to be: —

For the 26.5 ton train, 150 horse-power; for the 45.5 ton train, 134 horse-power; for the 64 ton train, 96 horse-power: the loss (due to leakage) increasing with the degree of exhaustion applied.

Finally he estimated the component parts of the resistance offered to the motion of the trains, and after making the proper allowance for gravity (1 in 115) and friction (10 lbs. per ton), a large surplus was found to be due to the resistance of the atmosphere. For example, with the 26.5 ton train, moving at 34.7 miles an hour, this residual resistance was found to be 78 horse-power out of 150. With the 45.5 ton train, at 25 miles an hour, it was 44 out of 134. And with the 64 ton train, at 16.75 miles, it was 11 horse-power out of 96.

Mr. Stephenson considered this last result as of great importance, and having a bearing much wider than the case in question. He says : —

In referring to the loss of power from the resistance of the atmosphere, it will be observed there is a very rapid reduction in the loss, as the speed is diminished, indicating most satisfactorily the excessive expenditure of power, and consequent augmentation of expense, in working at high velocities upon railways. This remark is of course equally applicable to all railways, whatever be the motive power employed, and it is here introduced only for the purpose of showing that the attainment of speed exceeding that which is now realised upon some of the existing lines of railway is a matter of extreme difficulty, and that the atmospheric system is not exempt from that wasteful application of power which high velocities inevitably entail. For although the resistance of the atmosphere to railway trains has been established for a long time, the limit which it is likely to put to every effort to obtain such velocities as have been generally believed to be within the reach of the atmospheric railway has not, I am sure, been sufficiently brought forward.

Mr. Stephenson also pointed out, as a result of his experiments, the necessity of working with only a moderate degree of exhaustion; as he was led to the conclusion that when the barometer rose to a certain height, the expansion of the air leaking into the apparatus must become fully equal to the total capacity of the pump, and no advance of the tube piston could be effected; this case occurred on the Kingstown and Dalkey Railway, with a height of barometer of 25.5 inches. ‘ This conclusion,’ adds Mr. Stephenson, ‘ which is unquestionably correct, points out the improvident expenditure of power when a high degree of rarefaction is required.’

Having thus explained the object and result of the experiments instituted on the Kingstown and Dalkey Railway, Mr. Stephenson proceeded to draw a comparison between the working of the atmospheric system and of other descriptions of motive power, with the view of showing their relative advantages and disadvantages.

The first comparison was with the stationary engine and rope. Mr. Stephenson chose the incline on the North-Western Railway, from Euston Square to Camden Town, nearly a mile long, and with an average gradient of 1 in 106, and which at that time was worked in this manner. He gave a table of experiments upon it, and showed, by an example serving for comparison in the two cases, that the waste of power on the Euston incline amounted to only 45 per cent, as against 74 per cent on the atmospheric plan. At the same time it was admitted that working a longer length of fine would make the comparison more favourable to the latter plan.

Next came the comparison with the locomotive engine. Mr. Stephenson took as an example the atmospheric train of 26.5 tons, moving at 34.7 miles per hour, at which rate he found the total loss of power by leakage, getting up the vacuum, and starting the train, equal to 53 per cent of the quantity developed by the engine. He then found that, when a locomotive drew a train of the same weight up the same gradient, its own gravity, friction, and atmospheric resistance, ‘ together with a further resistance arising from the pressure of the atmosphere against the pistons, peculiar to the working of a locomotive,’ would consume to waste 54 per cent of the total power developed. ‘ Therefore,’ infers Mr. Stephenson, ‘ the loss of power by the use of the locomotive engine under such circumstances appears somewhat to exceed that shown by the atmospheric system; this is, however, a most disadvantageous comparison for the locomotive engine, because the gradient far exceeds that upon which it can be worked economically.

‘Such a comparison,’ he says in another place, ‘ cannot be held as strictly correct, because the locomotive engine, as a motive power on steep gradients, is wasteful, expensive, and uncertain; therefore on a long series of bad gradients, extending over several miles, where the kind of traffic is such that it is essential to avoid intermediate stoppages, the atmospheric system would be the most expedient. The lightest trains taken upon the Kingstown and Dalkey incline, at the velocities recorded, probably exceed the capabilities of locomotive engines, and so far prove that the atmospheric system is capable of being applied to somewhat steeper gradients, and that on such gradients a greater speed may be maintained than with locomotive engines.’

As regarded lines of more moderate steepness, he reduced the Dalkey performance to what it might be held equivalent to on a level, in order to show that such a performance was exceeded on many locomotive hues; and he added the strong expression of his opinion that on hues of railways where moderate gradients were attainable at a reasonable expense, the locomotive engine was decidedly superior, both as regarded power and speed, to any results developed or likely to be developed by the atmospheric system.

Up to this point, the calculations and remarks in the. Report had reference solely to the question of power, entirely independent of the questions of expense or convenience, which therefore Mr. Stephenson next proceeded to examine, beginning with the cost of construction.

The advocates of the atmospheric system, knowing the great expense of the apparatus, had asserted it to be possible to work any reasonable amount of traffic with a single line. This assertion Mr. Stephenson disputed, showing that on a long line, if trains were despatched with sufficient frequency to carry the traffic both ways, the delay, by stoppages necessary for the trains to pass each other, would be so great as to defeat the object altogether. Hence he considered a double line absolutely essential for any considerable length of railway; and he also concluded that each line must be provided with its proper complement of engine-power. ‘ The intersections of the trains,’ he says, ‘cannot possibly be made to take place always at the same points, even on the supposition that each railway is worked independently of every other with which it may be in connection. When we introduce, in addition, the fact that several branch lines must necessarily flow into the main trunks; that no line can be worked independently; that the arrival of trains is, and must always be, subject to much irregularity, sometimes arising from their local arrangements, sometimes from weather, and at others from contingencies inseparable from so complicated a machine as a railway ; it must be palpable that two independent series of stationary engines are as indispensable as two independent lines of vacuum tube, for the accomplishment of that certainty, regularity, and despatch which already characterise ordinary railway operations.’

Coming to figures, Mr. Samuda, on behalf of the atmospheric system, had estimated for a single line of tube as follows :—

Vacuum Tube, with all its appliances . £3,342 Per Mile.
Engines £1,343 Per Mile.
Total £4,685 Per Mile.

Mr. Stephenson, considering a double line necessary, and that Mr. Samuda had not taken his engines powerful enough, altered this to—

Vacuum Tubes . £7,000 Per Mile.
Engines 4,000 Per Mile.
Total 11,000 Per Mile.

He then applied this, as an example, to the London and Birmingham Railway, 111 miles long, which would make the cost of the atmospheric apparatus amount to £1,221,000, whereas the capital expended on locomotives and all their contingent outlay was only £321,000, making a difference of £900,000 against the atmospheric system,

Mr. Stephenson admitted, that if that line had been originally laid out for the atmospheric plan, a saving of £900,000 might have been accomplished in the original design ; but he remarked that on other lines of railway where the gradients conformed more to the surface of the country, the excess of first outlay to adapt the atmospheric plan to them would be very heavy; and he gave "an example of a cheap railway for light traffic in Norfolk, where the application of the atmospheric system would have involved a cost so great as to render it totally in- applicable.

The next point considered was the cost of working, which, taking the London and Birmingham again as an example, Mr, Stephenson was of opinion would be greater by the atmospheric than the locomotive system in the proportion of £74,000 to £64,000 per annum.

Such were Mr. Stephenson’s conclusions as to the capabilities of the atmospheric system as a motive power, and the cost of applying it. He finally devoted a short space to the consideration of some other questions, scarcely of less consequence when the application of the system to daily practical purposes was discussed; namely, the speed attainable, the safety, the certainty, and the liability to casualty or derangement.

These were questions, he said, upon which widely different opinions might be entertained, but some of which could only be fairly appreciated by persons really conversant with the practical working of railway traffic.

As to the speed, he considered he had already proved that, though increased velocity might be obtained, it could only be done with an inordinate expenditure of power.

On the safety of the atmospheric system there could, he said, be little room for difference of opinion, as it might be stated to be nearly perfect; but he thought that further experience would much diminish the risk with locomotive engines.

But the question of certainty of action, Mr. Stephenson conceived, would be found to involve considerations militating most seriously against the plan, even though the first outlay and cost of working were in its favour.

‘ Each train,’ he says, ‘ in moving between London and Birmingham, would be passed, as it were, through thirty-eight distinct systems of mechanism, and it cannot be deemed unreasonable to suppose that in such a vast series of machinery as would be required in this instance, casualties occasioning delay must not unfrequently occur. If the consequences were cod- fined to one train, such casualties would be of small moment. but the perfect operation of the whole is dependent on each individual part, and when the casualties extend themselves not only throughout the whole line of railway, but to every succeeding train which has to pass the locality of the mishap,, until it is rectified, whether this occupies one hour or one week, the chances of irregularity must be admitted to be very great. The delay would apply to every train, whatever might be its destination, and to every railway in connection with that upon which the accident occurred. Such a dependency of one line of railway upon the perfectly uniform and efficient operation of a complicated series of machinery on every other with which it is connected, appears to me to present a most formidable difficulty to the application of the system to great public lines of railway; so formidable, indeed, that I doubt much whether, if in every respect the system were superior to that of locomotive engines, it could be carried out upon such a chain of railways as exists between London and Liverpool, or London and York.

‘This difficulty, which is insurmountable and inherent in all systems involving the use of stationary engines, was fully considered previous to the opening of the Liverpool and Manchester Railway, when the application, to that line, of stationary engines and ropes was contemplated; at that time the objection of the whole line being so dependent upon a part was maturely weighed, and decided to be most objectionable. In going through this investigation, I have again deliberated much on the feasibility of working such a system, but without any success in removing those obstacles which must interfere with the accomplishment of that certainty which has become indispensable in railway communication.’

Mr. Stephenson also referred to other objections; such as the chance of derangement of the tube by subsidence of the earthwork; the complication of working the traffic at intermediate stations; the difficulty of shunting, or of stopping the train on a sudden emergency, &c. &c. Of these, with many other objections of a minor character, he chose to take only a slight notice, as his wish was to call attention only to the main features of the invention, and to treat nothing as a difficulty which was not obviously inherent or irremediable in the atmospheric system itself.

Finally, Mr. Stephenson summed up the conclusions to which his investigation had led him in the following terms :—

I. That the atmospheric system is not an economical mode of transmitting power, and inferior in this respect both to locomotive engines and stationary engines with ropes.

II. That it is not calculated practically to acquire and maintain higher velocities than are comprised in the present working of locomotive engines.

III. That it would not in the majority of instances produce economy in the original construction of railways, and in many would most materially augment their cost.

IV. That on some short railways where the traffic is large, admitting of trains of moderate weight, but requiring high velocities and frequent departures, and where the face of the country is such as to preclude the use of gradients suitable for locomotive engines, the atmospheric system would prove the most eligible.

V. That on short lines of railway, say four or five miles in length, in the vicinity of large towns, where frequent and rapid communication is required between the termini alone, the atmospheric system might be advantageously applied.

VI. That on short lines, such as the Blackwall Railway, where the traffic is chiefly derived from intermediate points, requiring frequent stoppages between the termini, the atmospheric system is inapplicable, being much inferior to the plan of disconnecting the carriages from a rope for the accommodation of the intermediate traffic.

VII. That on long lines of railway the requisites of a large traffic cannot be attained by so inflexible a system as the atmospheric, in which the efficient operation of the whole depends so completely upon the perfect performance of each individual section of the machinery.

Appended to Mr. Stephenson’s Report was a statement by Mr. G. P. Bidder regarding the Blackwall Railway. This line was at that time worked by stationary engines and ropes, but the advocates of the atmospheric system had urged its adoption in preference.

Mr. Bidder, after describing the peculiar circumstances of the traffic on the line, showed satisfactorily that the atmospheric system could not be applied to it with advantage, chiefly from the necessity for frequent stoppages at intermediate stations, which could not be effected, or at least, if effected, would entail such delays as would be extremely inconvenient to the pubhc, and prejudicial to the interests of the hne.

Since 1849, the Blackwall Railway, having been extended and connected with other lines, has been worked by locomotive power.

Mr. Stephenson’s Report was published and widely circulated; but though it decided the Chester and Holyhead directors not to adopt the atmospheric system on their line, it does not seem to have checked its advance in public estimation; for the features of the scheme were so attractive and popular as to secure for it the evident favour, not only of railway authorities and the public generally, but also of a number of professional engineers. To the latter class the subject naturally proved a very interesting one; for at three several times, in the years 1844 and 1845, it was brought prominently forward and discussed at great length at meetings of the Institution of Civil Engineers, almost all the principal members of the profession taking part in the arguments either on one side or the other; and at a later period, when it was in action on the Croydon line, the same Institution promoted the appointment of a scientific committee to make experiments upon it— a design which, had it not been frustrated by the sudden and premature abandonment of the system on that fine, would undoubtedly have been of the greatest interest and importance in a scientific point of view.

Almost immediately after the date of Mr. Stephenson’s Report, the subject was brought forward in Parliament, by a bill promoted by the Croydon Railway Company for an extension of their line to Epsom, which it was proposed to work on the atmospheric plan. On the committal of this bill a long investigation into the merits of the system took place, extending from the 15th to the 21st of May, and embracing all that could be said for or against the plan. Mr. Cubitt, the engineer of the line, explained his reasons for adopting it, in which he was supported by Mr. Samuda, Mr. Gibbons of the Dalkey fine, and Mr. I. K. Brunel. Mr. Stephenson gave evidence against it, stating and explaining the arguments used in his report to the Chester and Holyhead Railway. The Committee, however, appear to have been satisfied of the practicability of the plan, as they passed the bill; and when it had gone through the other legal stages, steps were immediately taken to put the works into execution.

In the next year, 1845, the subject attracted still more prominently the public attention. This, it will be recollected, was about the time of the well-known railway mania, when speculation was excited to a degree unheard of before, and new fines were promoted in vast numbers from all corners of the empire. The atmospheric system, by promising to cheapen the construction of new lines, and to facilitate their formation, was too enticing to be overlooked; and consequently, among the multitudes of new lines introduced into Parliament at the commencement of the session of 1845, were many in which this system of propulsion was proposed to be adopted, and some of which indeed, by their inapplicability to locomotive traction, depended for their very existence on the feasibility of the plan.

Independently of the Epsom line, already sanctioned and in progress of construction, many others, of much public importance, were now proposed to be worked on this system— as, for example, one from Newcastle to Berwick ; continuations of the Epsom line directly to Portsmouth, of the Croydon line to Maidstone, Tunbridge, and Ashford, and of the Dalkey line to Bray, and a direct line from London to Northampton.

To have left the full discussion of the atmospheric principle to be undertaken in each separate case would, it was thought, lead to much difficulty and delay; and therefore, on the motion of Lord Howick (afterwards Earl Grey), a Committee of the House of Commons was appointed to investigate, once for all, the merits of the plan, and to report to the House thereon.

The Committee consisted of fifteen members, the Hon. Bingham Baring in the chair. They were appointed March 14, 1845, examined witnesses from April 1 to April 11, and made their Report on April 22; an instance of very remarkable expedition, showing the urgency they attached to the subject.

The first witness examined was Mr. Samuda, one of the patentees, who explained at great length the nature and advantages of the principle; stated what was being done to put it into operation on various lines; and answered objections that had been made against it.

Mr. Barry Gibbons, the engineer, and Mr. Bergin, the manager, of the Kingstown and Dalkey line, explained the working of the system there, and testified to its success.

Mr. Brunel supported the plan, and described the extensive use he was making of it on the South Devon line. Mr. (afterwards Sir) William Cubitt followed on the same side, and described his application of the atmospheric system to the Croydon and Epsom fines. The principle was also supported by Mr. Vignoles and Mr. Field, eminent civil and mechanical engineers, and by the Rev. Dr. Robinson of Armagh.

On the other hand, Mr. Robert Stephenson, Mr. Bidder, Mr. Nicholson, and Mr. Locke testified against the system.

The advantages of atmospheric propulsion, and the arguments in its favour, which have been already stated, were urged upon the Committee by the first set of witnesses, while the objections to it were principally those given in Mr. Stephenson’s report, to which, however, a few minor ones were added— as the loss of power by the friction of the air in the tube; the heating of the air in the pump during compression; the impossibility of making level crossings, or of having junctions with branch lines except at the principal stations; the great cost of running only few trains, as at night, and so on.

The Committee, after due deliberation and discussion among themselves, adopted a Report which is of sufficient importance to warrant its insertion here. It runs as follows, omitting some passages of minor interest:

The Select Committee appointed to inquire into the merits of the atmospheric system of railway have examined the matters to them referred, and have agreed to the following Report.

Your Committee have given their best attention to this interesting subject. Adverting to the great number of Railway Bills now in progress, they consider that one of the most practical results of this inquiry would be lost if their Report were delayed until after these bills had passed through Committee, and a decision had already been made on their comparative merits.

Your Committee have endeavoured therefore to present to the House, with as little delay as is consistent with the due discharge of their duty, the evidence which they have taken, and the opinions to which they have come, and they trust that their labour may not prove altogether useless to the Committees that have to decide on the particular railway schemes now pending.

The House are aware that a railway on the atmospheric principle is already in operation between Kingstown and Dalkey, in Ireland.

The first object of your Committee was to make a full inquiry into the result of this experiment. From Mr. Gibbons, Mr. Bergin, and Mr. Vignoles, gentlemen officially connected with the Kingstown and Dublin, and Kingstown and Dalkey Railways, they received the fullest and frankest evidence on all the points connected with their management.

From this evidence, and from that of Mr. Samuda, it appears that the Dalkey line has been open for nineteen months, that it has worked with regularity and safety throughout all the vicissitudes of temperature, and that the few interruptions which have occurred have arisen rather from the inexperience of the attendants than from any material defect of the system.

Your Committee find, moreover, that high velocities have been obtained with proportional loads on an incline averaging 1 in 115, within a course in which the power is applied only during one mile and an eighth.

These results have been displayed under circumstances which afford no fair criterion of what may be expected elsewhere; for in addition to the curves on the line, which would have been considered objectionable if not impracticable for locomotive engines, there are alleged to exist defects in the machinery and apparatus, occasioned partly by the difficulties of the situation, partly by mistakes inseparable from a first attempt, which very seriously detract from the efficiency of the power employed, for the remedy of which provision has been made in the experiments now in progress.

These are important facts. They establish the mechanical efficiency of the atmospheric power to convey with regularity, speed, and security, the traffic upon one section of pipe between two termini; and your Committee have since been satisfied, by the evidence of Messrs. Brunel, Cubitt, and Vignoles, that there is no mechanical difficulty which will oppose the working of the same system upon a line of any length. They are further confirmed in this opinion by the conduct of the Dalkey and Kingstown directors, who have at this moment before Parliament a proposition to extend their atmospheric line to Bray.

In addition to the witnesses already mentioned, your Committee have had the advantage of hearing the objections urged by Messrs. Nicholson, Stephenson, and Locke against the adoption of the atmospheric principle, and the grounds of their preference for the locomotive now in use.

Your Committee must refer the House to the valuable evidence given by these gentlemen.

It will be seen that great difference of opinion exists between them and the other witnesses to whom your Committee have before referred, both in their estimation of what has already been effected, and in their calculations of future improvement.

But without entering upon all the controverted points, your Committee have no hesitation in stating that a single atmospheric line is superior to a double locomotive line in both regularity and safety, inasmuch as it makes collisions impossible, except at crossing places, and excludes all the danger and irregularity arising from casualties to engines or their tenders.

Your Committee desire also to bring to the attention of the House a peculiarity of the atmospheric system, which has been adduced by the objectors to prove how unsuited it must be profitably to carry on a small and irregular traffic; namely, that the greatest proportion of the expenses of haulage on the atmospheric principle are constant, and cannot be materially reduced, however small the amount of traffic may be. This is, no doubt, a serious objection to the economy of the atmospheric system under the circumstances above alluded to. But on the other hand, as the expenses do not increase in proportion to the frequency of the trains, it is to the interest of companies adopting the atmospheric system to increase the amount of their traffic by running frequent light trains at low rates of fare, by which the convenience of the public must be greatly promoted.

Upon an atmospheric railway the moving power is most economically applied by dividing the weight to be carried into a considerable number of light trains. By locomotive engines, on the contrary, the power is most conveniently applied by concentrating the traffic in a smaller number of heavier trains. The rate of speed at which trains of moderate weight can be conveyed on an atmospheric line makes comparatively little difference in the cost of conveyance, while the cost of moving trains by locomotive engines increases rapidly with the speed.

Now when it is considered that we surrender to great monopolies the regulation of all the arteries of. communication throughout the kingdom, that it depends in a great measure upon their view of their interest when we shall travel, at what speed we shall travel, and what we shall pay, it becomes a material consideration, in balancing the advantages ensured to the public by rival systems, to estimate not so much what they respectively can do, but what, in the pursuit of their own emolument, they will do.

The main objections of the opponents of the atmospheric system seem to rest— first, on the supposed increase of expense of the atmospheric apparatus over and above the saving made in the construction of the road; secondly, on the inconvenience and irregularity attending upon a single line. With reference to the last point, your Committee felt it their duty to direct their first attention to the question of security, and they have already stated that there is more security in a single atmospheric line than a double locomotive. They may further observe that they find the majority of the engineers who have been examined are decidedly of opinion that any ordinary traffic might be carried on with regularity and convenience by a single atmospheric line.

With respect to expense, and to some other contested points, your Committee do not feel themselves competent to report a decided opinion. It would scarcely be possible at the present time to institute a fair comparison of a system which has had fifteen years of growth and developement, with another which is as yet in its infancy. That comparison would, after all, be very uncertain; it must depend much on details of which we are ignorant, much on scientific knowledge which we do not possess. There are, however, questions of practical importance, having reference to the present state of the Railway Bills before the House, to which your Committee consider themselves bound to advert.

There is a doubt, raised in the Reports of the Board of Trade, whether the atmospheric system has been sufficiently tested to justify the preference of a line which can only be worked on the atmospheric system, or which presents gradients less favourable than a competing line for the use of the locomotive engine.

If it were practicable to suspend all railway legislation until the result of the Devon and Cornwall, and of the Epsom and Croydon atmospheric lines were known, it would be perhaps the most cautious and prudent course to wait that result; but such a course, independent of all considerations of expediency, is evidently impracticable. Your Committee venture therefore to express their opinion to the House, that in deciding between competing lines of railway, those which have been set out to suit the atmospheric principle ought not to be considered as open to valid objections merely on account of their having gradients too severe for the locomotive; nor should they be tested, in comparison with other lines, solely by the degree of their suitableness to the use of the locomotive.

No doubt, in matters like these, experience alone can decide the ultimate result; but your Committee think that there is ample evidence which would justify the adoption of an atmospheric line at the present time. All the witnesses they have examined concur in its mechanical success.

Mr. Bidder says: ‘I consider the mechanical problem as solved, whether the atmospheric could be made an efficient tractive agent. There can be no question about that, and the apparatus worked, as far as I observed it, very well. The only question in my mind was as to the commercial application of it.’ Mr. Stephenson admits that under certain circumstances of gradients (1,315), and under certain circumstances of traffic, without reference to gradients (1,204), the atmospheric system would be preferable.

While your Committee have thus expressed a strong opinion in favour of the general merits of the atmospheric principle, they feel that experience can alone determine under what circumstances of traffic, or of country, the preference to either system should be given.

This decision, so favourable to the atmospheric system, cannot be wondered at. The preponderance of evidence, even of engineers, was undoubtedly in its favour; and, however we may now be convinced of the validity of the objections urged against it, and of the superior judgement of the witnesses who opposed it, it was not to be expected that a Committee so composed should be in a position to attach such weight to these objections as to invalidate the concurrent and positive testimony adduced on the other side.

Supported, therefore, by so powerful and public a recommendation, we should be prepared to expect that the atmospheric system would soon have been extensively introduced, at least on new lines— if, indeed, it did not supersede the established plans of locomotion on old ones; for as has been already stated, the inducement today down new hues with gradients and works adapted for the plan must have been very strong.

But this official recognition of the merits of the system forms the culminating point of its history; for, strange to say, from this event we have only to trace its continual decadence, and, within but a few years afterwards, to chronicle its abandonment altogether.

The examination of the atmospheric bills in Parliament, in the following session of 1845, proceeded in due course ; but the labours of Lord Howick’s Committee do not seem to have had the effect intended; for the opponents of the atmospheric system— who, though small in numbers, were very energetic and determined—did not choose to yield to their decision, and the contest had to be renewed in every Committee on every bill.

One of the most important of these contests was that for the line from Newcastle-upon-Tyne to Berwick, in which a single atmospheric line was opposed to the double locomotive railway projected by George Stephenson and his son. The battle of these two rival fines was fought very obstinately and at great length before the Committee of the House of Commons; and in July 1846 they reported that, although they did not feel called upon to express an opinion on the relative merits of the atmospheric and the locomotive systems, or on their comparative applicability to railways in general, still as the evidence negatived the sufficiency of a single fine to convey the required traffic, they preferred the locomotive double fine, which was eventually adopted.

The Bill for the Epsom and Portsmouth fine passed on the atmospheric principle, but was never carried into execution: all the other Bills were either lost or abandoned.

It now only remains to mention the several cases where the atmospheric system has been applied in actual practice ; there are five in number.

The first of them, the experimental half mile on the small railway at Wormwood Scrubs, may be dismissed very briefly. It was, as has been stated, set to work in June 1840. It was not intended for traffic, as the line was not commercially used at that time; but it was worked experimentally. During the first year trips were run regularly twice a week, to which the public were admitted free; and subsequently experiments were made at various intervals during or 2 years more; after which the apparatus was removed.

Next in order comes the Kingstown and Dalkey line, of which a description has already been given. It was first tried in August 1843, and commenced working regularly towards the end of September; but in consequence of some legal difficulties it was not opened for public traffic till some months later. During the interval, however, it was at work, carrying passengers without charge; and any persons who had an introduction, or any special claim, were allowed to make experiments in any manner they desired, without expense to them: the public travelling at the same time for amusement in very large numbers. In March 1844, it began running for regular commercial traffic, and worked for several years, conveying great numbers of passengers to and fro, with perfect safety and considerable speed. On occasions of any peculiar attraction, the double journey was performed every ten minutes, from 7 A.M. to 11 P.M.

About 1855 the Dalkey, Dublin, and Kingstown property was leased to the Dublin, Wicklow, and Wexford Railway Company. The portion between Kingstown and Dalkey was included, and was extended to Bray, where it joined the direct Dublin and Wicklow line; and as it would have been obviously inconvenient to have an isolated portion, of one mile and a half in length, of atmospheric propulsion in the middle of a system worked by locomotives, the tube was taken up, and the line enlarged, and made a homogeneous part of the extended system.

The third application of the atmospheric principle was upon the London and Croydon Railway. Reference has been made to the Act obtained in 1844 for an extension of that line from Croydon to Epsom, which the Company proposed to work on the atmospheric system. But as the line from Croydon to London was becoming much occupied by the Brighton and the South Eastern Companies, both of which ran over its whole length, it was considered expedient to lay down an additional or third line of rails alongside the other two, over this distance, so as to give an independent accommodation to the Croydon and Epsom traffic. This was-considered a favourable portion on which to test the invention; and as this line could be sooner constructed than the new one beyond Croydon, great efforts were made to have the atmospheric apparatus at work upon it as early as possible: and it was opened for a distance of five miles, from Forest Hill to Croydon, in the latter part of 1845. From London to Forest Hill the atmospheric apparatus was not completed, the trains being worked by locomotives, and run into a siding for attachment to the piston carriage of the atmospheric tube.

The tube, which was 15 inches internal diameter, was divided into two lengths— one of 3 miles from Forest Hill to Norwood, and the other of 2 miles from thence to Croydon— there being steam engines of 100 nominal horse-power, with air pumps, placed at each of the three stations. In one place the railway crossed over the Brighton main line by a viaduct, with gradients on each side of 1 in 50.

For a short time after the apparatus was set to work it was employed in running empty trains at certain intervals during the day, to give the public an opportunity of seeing the new mode of conveyance. It is stated that trains of nineteen carriages were conveyed at 30 to 35 miles an hour, or even at greater speed under favourable circumstances; but the vacuum employed was high, being 24 to 26 inches, and the power consumed in pumping was large. With lighter trains velocities of 60 miles an hour were attained.

On January 19, 1846, it commenced working for regular traffic; but, though generally successful, frequent interruptions took place from various accidents; principally through defects in the stationary engines, which appeared not to be well adapted to the purpose they had to serve.

In May the number of trains was increased from thirty-two to thirty-nine per diem, and the regularity was generally improved, though some difficulty still occurred in getting over the steep incline.

The summer discovered an unexpected weakness, for the June sun, giving a temperature of 131° over the pipe, acted so powerfully upon the waxy sealing composition of the valve, that it was difficult to keep it tight against the pressure of the atmosphere ; and on this, as on other occasions, the aid of the locomotive had to be called in. The valve itself was also defective, and a new one had to be inserted, as well as a new sealing material to be compounded, which proved successful, and was suitable to resist the effect of both heat and cold. The apparatus was set to work again in July, and a good regularity attained. A record of three trips on the 21st of that month shows satisfactory results. A train of 50 tons attained a maximum speed of 30 miles an hour, and one of 22 tons, 64.25 miles, the vacuum in all cases being 19 inches.

In this year the amalgamation of the Croydon Railway with the London and Brighton line took place. The directors of the former, in giving up their charge. August 26th, remarked that, ‘ though the atmospheric system had not been free from those difficulties which usually attend the introduction of all new inventions, and though the working expenses had necessarily been very great, still it was progressing satisfactorily.’ At the first meeting of the amalgamated companies on August 19, the directors also stated that ‘the working progressed satisfactorily, and attained daily a greater degree of regularity, and that there was every reason they should have confidence in it.’ Considering, however, the thing still as under experiment, they resolved, on the recommendation of Mr. Cubitt, their engineer, to open the Croydon and Epsom extension, in the first instance, as a locomotive line, until the merits or defects of the new system should have been more thoroughly tried.

In November the manager of the line was directed to make out a statement of the cost of working the system, which he did, much in its disfavour; but his statement was called in question by Mr. Samuda, who contended that the facts did not warrant this disparaging judgment.

During the winter the number of trains was thirty-six daily. In January 1847, a further portion of the atmospheric tube was finished towards London, and on the 14th of that month a trial trip was made, preparatory to the opening. From New Cross to Forest Hill the fine ascended for nearly the whole distance an incline of 1 in 100, and the train ran up this and on to Croydon in a satisfactory manner.

In February some stoppages took place in consequence of snow and frost, and the locomotive had again to be resorted to; and at a meeting on the 19th of the same month, the second after the amalgamation, the directors reported that, with a view to determine the amount of expenditure, and at the same time to test practically the value of the system, they had entered into an arrangement with Mr. Samuda for working the atmospheric traction upon a contract for a fixed sum and during a certain period. Some of the shareholders at this meeting strongly advocated the abandonment of the plan; to which it was answered that it had been proved both practicable and efficient, but that the directors would not consent to continue it longer than they thought right.

From this time it seems to have worked well; and a committee of scientific men was appointed by the Institution of Civil Engineers to make experiments on it with a view to determine its powers; when an event occurred which we may best describe by an extract from one of the railway journals of the period, dated May 8, 1847.

Engineering London was suddenly thrown into unusual excitement on Tuesday last by the announcement that the Croydon Atmospheric Pipes were pulled up and the plan abandoned.

On making inquiry we found that it had been decided to abandon the system, that the atmospheric was not in operation, that locomotives were doing the work, and that the atmospheric was doomed'.

We confess our surprise at this sudden resolve. The same resolve might have been taken any time these twelve months with more show of reason than appears now on the face of the question. Never before was the atmospheric doing so well, going so regularly, working so economically. The directors have for a couple of months been working a contract with Mr. Samuda, which contract gives them atmospheric power at less cost than the locomotive; and Mr. Samuda is said to have been well pleased with his contract and the public service well performed.

We are the more sorry for this resolution, because, although we have from the beginning been regarded by the advocates of the atmospheric system as its inveterate enemies, we have really opposed only what appeared to us the errors of the system; and while opposing its erroneous application, we have earnestly supported its having a fair trial. That trial we thought it would have had on the Croydon, and we are disappointed at this sudden resolution of the Board, which will, we think, give the advocates of the system something to complain of, and deprive all parties of the advantage of an unbiassed decision.

The explanation given by the directors is in then report of August 10, where they say : ‘ From the insufficiency of power by atmospheric traction to work the Epsom in addition to the Croydon traffic, your directors, by the advice of their consulting engineer, have substituted locomotive power.’ This ‘insufficiency’ arose from the vacuum tube being too small. The temptation to save as much as possible in the first cost of the apparatus, of which the tube formed such a large item, led to its being fixed at dimensions which, though probably large enough for the traffic existing at the time it was designed, did not allow for much increase. Hence, when larger loads had to be conveyed, it became necessary to work the vacuum higher, which, as had long before been predicted by Mr. Stephenson, brought the elements of leakage and friction into most disadvantageous operation. Mr. Samuda himself always stated the most eligible vacuum to be 15 or 16 inches, but with the size of tube on, the Croydon line this vacuum had to be much exceeded when the loads became heavy.

It is possible that this difficulty might have been overcome by dividing the loads, and running trains at more frequent intervals : but there was another motive which probably acted more strongly with the directors than the ‘ insufficiency of power.’ When the atmospheric system was originally adopted by the Croydon Company, their new or third line was to be an isolated one, doing the Croydon traffic only; but the case was materially altered when this became a trunk line for the Epsom traffic, and for probable future extensions.

Moreover, there had arisen a new management, who had not taken any part in the anterior proceedings. The Croydon Company had sold themselves and their undertaking to a more powerful body, owning a large and important group of hues all worked by locomotive power, under one management and with one stock, except this small piece of atmospheric line, which was so isolated as to be obliged to be connected with locomotive lines at each end.

No doubt, therefore, the Brighton directors were only too glad of any reasonable excuse that might offer for throwing the thing overboard altogether. This excuse came in the sudden pressure of the Epsom race week; and in spite of the improved behaviour of the apparatus, in spite of the beneficial contract with Mr. Samuda, and in spite of the absurdity of incurring all the cost of the experiment without gaining any intelligible result therefrom, the atmospheric system was forthwith suddenly condemned ; the pipes were taken up and sold for old iron; the engine houses were pulled down and carted away as old bricks; and thus ended the trial of the atmospheric system on the Croydon Railway.

The next application to be recorded was on the South Devon Railway, a line running between Exeter and Plymouth. The Act incorporating the Company was passed in July 1841; and immediately afterwards a proposal was made by the promoters of the atmospheric system to apply it on that railway. The question was referred to Mr. Brunel, the engineer, who from his examination of its working on the Wormwood Scrubs and the Kingstown lines, came to such a favourable judgment upon it as induced him to recommend it for the line in question, which, having in some parts very difficult gradients and curves, offered a good opportunity for the display of its advantages. His view was confirmed by a committee of the directors, who had been deputed also to examine the working of the system ; and it was accordingly resolved to apply it upon the whole fine. The railway was laid out expressly for the system, having a single line only, with rails weighing 50 lbs. to the yard, and with bridges and viaducts lighter than those on a locomotive line, and otherwise different in construction.

It was decided to commence the working on the portion of the fine between Exeter and Newton - twenty miles with easy gradients. The pipe over this part was 15 inches diameter, and was in six divisions, with a pumping engine at each station. On the steeper and more difficult parts of the line, between Newton and Plymouth, having gradients of 1 in 50 and 1 in 42, it was proposed to have larger pipes, with an expanding piston. The tubes on this line were placed below the level of the rails, to facilitate the formation of level crossings ; and the piston was made to lift up when required.

From the desire to profit as much as possible by the experience acquired on the Croydon Railway, and from other causes, the manufacture of the atmospheric apparatus progressed very slowly; and in the beginning of 1846, a portion of the line being otherwise ready, the engineer decided not to delay the opening any longer, but to commence the passenger traffic with locomotives, which was done from Exeter to Teignmouth on May 30, 1846.

In the beginning of 1847 the stationary engines were erected, but it was April before any length of the atmospheric system was completed, the first trip being satisfactorily made from Exeter to Dawlish, 12.5 miles, on the 24th of that month.

In August 1847 it was ready as far as Teignmouth, 15.25 miles, and experimental trips were run over it with considerable speed, ease, and precision. With a 30 ton train a speed of 67 miles an hour was obtained; with 50 tons, 60 miles ; with 100 tons, 37 miles. In September the general traffic was worked by it over this distance with apparent satisfaction to the public. Towards the end of the year it was finished to Newton, and after several successful experimental trials it was publicly opened January 10, dispensing with the locomotives, and running with speed and regularity.

The apparatus, however, appeared liable to some sources of trouble, for at the general meeting in February 1848 Mr. Brunel reported that, notwithstanding numerous difficulties, he thought he was in a fair way of shortly overcoming the mechanical defects, and of bringing the whole into regular and efficient practical working, so as to be enabled to test its economy, which its incomplete state had not till then allowed him to do. At this same meeting also, the directors announced that, although the atmospheric works were in progress from Newton to Totness, a distance of nine miles, comprising difficult ground and steep inclines, they had decided to delay extending the system beyond the latter place (excepting only for assistant power on certain inclines) until experience should have afforded unquestionable data upon which to estimate its advantages, and should have confirmed the favourable opinion which the directors continued to entertain of its practical efficiency. In the interim it became necessary to strengthen the works, so as to fit them for locomotive traffic ; and this being done, the line was gradually finished from Newton towards Plymouth, and was opened, with locomotive power, to the immediate vicinity of the latter place in May 1848.

By this time it was found that the cost of working the atmospheric system had been much greater than the directors had reason to anticipate, and, moreover, that serious defects were beginning to manifest themselves in the mechanism of the longitudinal valve, the leather of which was undergoing an unexpected and rapid destruction. These serious considerations led the Board, in July, to refer the investigation of the whole subject to the special consideration of a committee, who for many weeks devoted their attention to it, in constant communication with the engineer. The result of their labours caused the directors, at a general Board meeting held August 28, 1848, to pass the following resolution :—

That the very heavy expenses incurred in working on the atmospheric principle between Exeter and Newton, arising in part from the imperfect state and rapid decay of the longitudinal valve, and in part from other causes affecting the system, render it necessary to suspend the employment of it, at the charge of the Company, until the patentees and Mr. Samuda shall have adopted some means, to the satisfaction of the directors, for relieving the Company from the loss consequent upon working under such disadvantages.

It was shown, however, by a document subsequently circulated by the Board, that the defect of the longitudinal valve was not the only difficulty of importance to be overcome. Many others were experienced which weighed greatly on the question of continuing the system :—

1. The necessity for dividing the passenger trains, and reducing the weight of the goods trains, to avoid the chance of all unusually heavy loads.

2. The loss of engine power throughout the line, whenever delays arose in the arrival of the trains; it being necessary, in the absence of any telegraphic communication, to keep up the vacuum, at enormous cost, until it was required to be used.

3. The other difficulties of working in immediate connection with a main line of near 200 miles, worked upon another system.

4. The probability, if not (under the circumstances of the Company) the certainty, that the atmospheric system could not be adopted on the whole line to Plymouth.

These difficulties, added to the cost of working, and the defective state of the valve, were found so formidable, that the continuance of the atmospheric mode of propulsion, upon an isolated length of twenty miles, connected at each end with lines worked on a different system, became all but impracticable.

In accordance with their resolution, the directors stated, in their report to the general meeting on August 29, that ‘ Without pronouncing any judgement as to the ultimate success of the atmospheric system, and whilst they are prepared to afford to the patentees and other parties interested in it the use of their machinery for continuing their own experiments, they have agreed with Mr. Brunel that it is expedient for them to suspend the use of the atmospheric system until the same shall be made efficient at the expense of the patentees.’

The operation of the system was accordingly brought to a close on September 9, 1848, and the line thenceforward was worked throughout by locomotives only.

But by far the most complete trial of the atmospheric system has been made in France; and as it does not appear that any account of this experiment has been published, the circumstances may be stated in some detail.

It appears that the system had at an early period excited some interest in that country, and a French improvement, of much ingenuity, was proposed in its machinery. This was the invention of M. Hallette, a manufacturing engineer of Arras. It was a new kind of longitudinal valve for the vacuum main, consisting of two small inflated elastic tubes, fixed in grooves on each side of the longitudinal opening on the top of the pipe, and between which the rod attached to the piston should slide, the tubes closing again behind it by their own elasticity as it passed along. M. Hallette laid down, at his own expense, an experimental tube, which exhibited his invention in action, and which is said to have worked well; but the ingenious inventor died in 1846, and his project never proceeded farther.

When the Kingstown and Dalkey line was first set to work, the French Government sent M. Mallet, one of the divisional inspectors of the Fonts et Chaussees, to examine its working. His report, which has been translated and published in England, is dated January 10, 1844 : his favourable account of the system appears to have determined the Government to try it in France, and a sum of 1,800,000 francs was accordingly voted for the cost of the necessary apparatus.

The railway on which it was decided to make the trial was that from Paris to St. Germain. This fine is altogether about 12.5 miles long. At the forest of Vesiuet, about 11 miles from Paris, it crosses the Seine, and from thence ascends by a rapid acclivity nearly 170 feet to the plateau on which the town of St. Germain stands. It was on this last 1| mile that the atmospheric system was applied. The length over which the tube extended was 2,230 metres. For the first 390 metres the fine was nearly level; the following 840 metres consisted of a series of inclines, beginning with 1 in 200, and gradually increasing to 1 in 30; and the last 1,000 metres was uniformly 1 in 28.75. On this steep part there was also a curve of 397 metres radius and 400 metres long; two curves on the lower portions were 1,000 metres radius.

The line was double, but the tube was only placed on the ascending line, the trains running down the other line by their own gravity.

The tube was 63 centimetres (about 24.5 inches) internal diameter, calculated for a maximum load of 70 tons. It was of cast iron 2 centimetres thick, strengthened by ribs, and having large feet cast on the lower part to fasten it down. The rails were fixed on longitudinal sleepers, and the tube rested upon the cross transoms which retained the longitudinal timbers in gauge. The longitudinal valve and the other parts of the apparatus were similar to those used in England.

There were two high pressure exhausting engines of 228 horse-power each, which were calculated to cause the ascent of the trains in five or six minutes.

The Company at first proposed to get the apparatus made in France, but were obliged ultimately to have the pipes cast in England. They were put in hand in the beginning of 1846, and the works of the line were ready in the autumn of that year; but by delays in the manufacture of the propelling apparatus the line was not opened for traffic till 1847.

The money voted by government paid for the tube and the engines; the remainder of the outlay, amounting to about 3,200,000 francs, was borne by the Railway Company.

The traffic consisted of passenger trains every hour of the day, for sixteen hours, giving sixteen trains per diem in each direction.

For about six years the average weight of the trains was about 35 tons, and the service was performed with great regularity; but after that time the traffic began to increase, the weight of the trains gradually augmenting to 50 or 60 tons, the consequence of which was the introduction of irregularities in the working. The causes of these irregularities were well investigated. The principal one was not chargeable to the system, and might easily have been remedied—namely, the inadequacy of boiler power in the stationary engines; but the loads soon began to approximate closely to the maximum limit of power of the apparatus, and as it was not always practicable to determine beforehand the exact weight of the train, it frequently happened that trains were sent up, on Sundays and fete days, of a weight touching closely upon this limit—even although, on arriving at the foot of the steep incline, the high vacuum of 70 to 72 centimetres (28 inches) was obtained in the tube. The natural result of this close working was, that if, as occasionally happened, the train was a little heavier than was calculated, or if any accidental increase to the resistance arose, the power proved insufficient for the traction, and the train came to a stand, or at least did not approach the terminus with the velocity necessary to shoot it up to the platform after the pressure had ceased to operate on the piston. The exhaustion varied usually from 40 centimetres (15.5 inches) to 72 centimetres, according to the weight of the train; and a singular coincidence was remarked on this-line— that the number of centimetres of exhaustion accurately denoted the number of tons weight which that degree of exhaustion would convey. The speed was slow upon the steep incline, but the trip was performed regularly in five or six minutes, as intended. Frost and snow were found to have a prejudicial effect on the valve: the leather hardened, ice or snow insinuated itself into the interstices, and the result was increased leakage and extra trouble to keep the machine in efficient action.

After all, however, so long as the haulage power was not overborne by the weight of the trains, the traffic went on pretty well, and the system continued in tolerably successful use for nearly fourteen years— namely, till 1860 — during the whole of which time there had never been a single accident or suspension of the service.

At this time it was found that serious repairs were required to the permanent way, the timber sleepers being decayed. The question then arose whether it might not be preferable to do away with the atmospheric system and to work the incline with locomotives like the rest of the line; and the following reasons seem to have been considered of sufficient weight to warrant this determination being adopted:-

First, the tractive power was obviously becoming more and more insufficient to work the constantly increasing traffic. Attempts had been made to increase the number of trains to three per hour during the heaviest pressure; but this led to difficulties at the stations, and it had become necessary on special days to get help from locomotive engines constructed for the purpose. Moreover, in the last year of working, a new element had been introduced, tending still farther to limit the useful power of the apparatus. The carriages had at first been veiy light, made especially for the purpose ; but it was found desirable to assimilate them to the other stock, and so to make them heavier, which of course, under the limit of weight, diminished the accommodation afforded for passengers by each train. And with this insufficient power, particularly considered in reference to a still farther prospective increase of traffic, there was no chance of any available remedy, if the plan was to be retained. The exhaustion had been carried to its utmost possible extent, and no alternative remained but to lay down a new tube of larger size and engines of larger power, which was clearly out of the question, from its enormous expense and the dead loss of all the expenditure previously incurred.

In the second place, the working expenses had been found very heavy; and although an accurate comparison could not then be made, it was believed that the incline could be worked by locomotives for less expense. The forcing up of the exhaustion, necessary to do the increased work, had augmented disproportionately the consumption of fuel; and as coals had latterly been very dear, the cost of working had showed to great disadvantage.

Then, thirdly, the improvements made in locomotives in late years had removed all doubt as to the practicability of applying them effectively on the steep incline, which could not have been attempted, with much chance of success, when the line was originally laid down.

These arguments appear to have had sufficient weight to lead the directors to abandon the atmospheric system of traction. The tube was accordingly taken up ; and the incline is now worked with powerful locomotives constructed expressly for the purpose, and which are said to be able to draw trains of 120 or 130 tons up the incline at less cost than on the former plan.

Such is the history of this remarkable scheme, which, as regards the magnitude of its pretensions, and the interest it excited, has no parallel in railway history. It is scarcely likely to be revived, and therefore it would be useless now to reopen a discussion upon it. But it may not be out of place, to add a few remarks on the results of the trials made.

We should naturally look to these trials for evidence on three main points— namely, first, the mechanical efficiency of the system as a propelling power; secondly, its economy; and thirdly, its general applicability to railway traffic.

With regard to the first head, we can scarcely avoid the conclusion that the trials were, at least, sufficient to establish it as an efficient means of propulsion, considered in a mechanical point of view.

Mr. Stephenson, who was no mean judge in such matters, always testified, with the candour and liberality that distinguished his character, to its mechanical success, and indeed never called its efficiency in question; and Mr. Bidder declared he considered the mechanical problem as solved beyond doubt.

On the Dalkey fine, the system worked the traffic regularly for eleven years. The Croydon experiment was attended with many vicissitudes, and formed in fact the principal school for the testing and improvement of the machinery on a large scale; but at the time the system was abandoned the mechanical defects had been in a great measure overcome, and it was working more satisfactorily than it had ever done before; and it is evident that the causes for its discontinuance, on this fine, arose more from general policy than from mechanical considerations.

The atmospheric system on the French fine worked, while moderately loaded, with great certainty; it was only when it began to be taxed too near the maximum Emit of its capability that irregularities occurred; but as, even under all circumstances, it worked for sixteen years without a single accident or suspension of the service, it is clear that no serious objection on mechanical grounds can have appeared.

On the South Devon line the regularity, speed, and safety were unquestioned. Great prominence was, indeed, given to the defective state of the longitudinal valve, as a reason for its discontinuance ; but had this been the only reason, it is difficult to conceive that, under the skill of such an engineer as Mr. Brunel, the same perseverance that had overcome the difficulty on the Dalkey and French lines would not have succeeded on this line also. We have seen, however, that other reasons obtained for the abandonment of the atmospheric system, and there is little doubt that these had more weight in the decision than any mechanical inefficiency.

Great credit is due to the inventors and original engineering promoters of the scheme for the perfection to which it was brought. The original perception of the practicability and advantages of a plan, which, to most minds, would have seemed only a wild vision, was in itself no common merit; and considering the entire novelty of the whole system and the absence of anything like precedent, the mechanical ingenuity and practical skill exhibited in designing and carrying out the details, was such as to place the contrivers in the highest rank of mechanical engineers, and to elicit the warmest commendation from even the opponents of the plan.

On the question of the economy of the system, the evidence is less satisfactory. In almost every instance the working expenses were complained of as very high ; and although the circumstances were in no case such as to render the result absolutely conclusive, we may at any rate consider the question of economy as standing where the arguments of Mr. Stephenson left it; if not indeed that his opinions were rather confirmed than disproved.

Then, thirdly, as to the general applicability of the system to railway traffic— it would seem that the fact of the entire abandonment of the system in every case is, to a certain extent, an argument pointing to a negative conclusion. If the invention had really promised to be beneficial, it is difficult to believe that it would not have been more fully persevered in; and we can only conceive its abandonment to have been dictated by a strong practical feeling that, even though further perseverance might establish its mechanical and economical success, it would still be found, on other grounds, an ineligible means of locomotion.

It will be seen that Mr. Stephenson’s principal objections to the system (apart from the cost) referred to its application to long lines. He urged that for any considerable length of railway, a double line with a complete double apparatus was absolutely essential; and that even with this, and though the economy were in its favour, yet on railways of large extent, there must exist conditions which would militate against its certainty of action, and which must disqualify it for being an appropriate means of railway traffic. Now it is quite clear that none of the trials actually made were of a nature to touch these objections. The longest line tried—the South Devon—had none of the characteristics of traffic on large trunk lines to which Mr. Stephenson’s reasonings applied, and therefore we must consider that his arguments on this head remain in full force, notwithstanding anything that has been done.

The immediate cause of the abandonment of the system, sooner or later, in every case where it has been tried, appears to have lain in its inflexibility—its want of elasticity—in its incapability of adapting itself to the changeable requirements and circumstances of a variable traffic — in its very peculiar nature, so uncongenial to the established habits of railway people—and in the great difficulty of bringing it to work conveniently and harmoniously in conjunction with other systems of railway traction. If we could conceive a line of railway isolated from aU others, and where the traffic should be perfectly uniform in amount and regular in time, possibly, as Mr. Stephenson admitted, the atmospheric system might be there applicable with advantage; but such a line would be an exceptional one; and certainly none of the railways on which it has been tried have approximated to these conditions.

An examination will show that, in every case, the most urgent reasons for the abandonment of the plan lay, either in the increase of traffic beyond what the tube could work, or in its isolated condition between locomotive lines at each end, which rendered the break of the system of haulage peculiarly disadvantageous, and fraught with such inconveniences as the proprietors would not submit to. On the French line the former of these objections prevailed; on the Dalkey and South Devon the latter; on the Croydon line both combined.

The inflexible and unaccommodating nature of the system was often and strongly insisted upon by Mr, Stephenson as a most powerful objection to it, applying indeed to every system of haulage by stationary power. It had been prominent in the original discussions on this subject in 1830, and it was obvious that the atmospheric system was only a renewal of the old proposition in a new form.

The system aimed at too great a change. It was not a mere improvement in things already existing — it was an entire revolution; a total subversion of the established mode of conducting the traffic, and a substitution of an entirely new plan: we cannot therefore wonder that it met with great opposition; nor could it be expected that anything short of the most complete and triumphant superiority could establish it. Railway people had become attached to the locomotive from its extreme convenience; and the change to a more rigid and limited plan was certainly not likely to find favour. There may be something in the national English independence of character which led railway officials to prefer a system that they could manage and vary with full liberty, to one in which they would aU become, as it were, mere parts of one huge machine.

For railways, generally, the locomotive appears now too well established to be liable to farther opposition from any modification of stationary power. It is true that it is, and must ever be, subject to many disadvantages inherent in the travelling form of the machine; but, considering the great improvements which have been made in it of late years, and its modern success in cases where its application was long considered impossible—and taking into account its versatile adaptability to variations of traffic; its admirable suitability to sudden emergency ; and its wonderful convenience of management and control— we think there can now be little dissent from the opinion so resolutely maintained by Mr. Stephenson, that the system of traction which rendered his father’s name famous is the only one well fitted for general use upon railways. W. P.

It may be useful to put on record the following list of published authorities made use of in this chapter: —

Acta Eruditorum. Leipsic 1688.

A New Method of conveying Letters and Goods with great Certainty and Rapidity by Air. By G. Medhurst, Inventor, Patentee, and Proprietor, 1 Denmark Street, Soho. London 1810.

Calculations and Remarks tending to prove the Practicability, Effects, and Advantages of a Plan for the rapid Conveyance of Goods and Passengers upon an Iron Road, through a Tube of Thirty Feet in Area, by the Power and Velocity of Air. By G. Medhurst, Inventor and Patentee, Denmark Street, Soho. London 1812.

On Facility of Intercourse. By John Vallance of Brighton. London 1824.

A New System of Inland Conveyance for Goods and Passengers, capable of being applied and extended throughout the Country, and of Conveying all kinds of Goods, Cattle, and Passengers, with the Velocity of Sixty Miles in an Hour, at an Expense that will not exceed the One-fourth Part of the Present Mode of Travelling, without the Aid of Horses or any Animal Power. By George Medhurst, Civil Engineer, Denmark Street, Soho. London 1827.

A Treatise on the Steam Engine, Historical, Practical, and Descriptive. By John Farey, Engineer. London 1827.

Report to the Directors of the Liverpool and Manchester Railway on the Comparative Merits of Locomotive and Fixed Engines as a Moving Power. By James Walker and J. U. Rastrick, Esq., Civil Engineers. Liverpool 1829.

Observations on the Comparative Merits of Locomotive and Fixed Engines, as applied to Railways: being a Reply to the Report of Mr. James Walker to the Directors of the Liverpool and Manchester Rahway, compiled from the Reports of Mr. George Stephenson. With an Accoimt of the Competition of Locomotive Engines at RainhUl in October 1829, and of the subsequent Experiments. By Robert Stephenson and Joseph Locke, Civil En^neers. Liverpool 1830.

Clegg’s Patent Atmospheric Railway. London 1839.

Clegg and Samuda’s Atmospheric Railway. London 1840.

Irish Railways. The Atmospheric Railway. A Letter to the Rt. Hon. Lord Viscount Morpeth. By James Pirn, jun.. Treasurer of the Dublin and Kingstown Railway Company. London 1841.

The Atmospheric Railway. A Letter to the Rt. Hon. the Earl of Ripon, President of the Board of Trade, &c. &c. By James Pirn, M.R.I.A. Treasurer of the Dublin and Kingstown Railway Company. With Plates. London 1841.

A Treatise on the Adaptation of Atmospheric Pressure to the Purposes of Locomotion on Railways. With Two Plates. By J. D’A. Samuda, London. (The date on the title-page is 1844, but the real date of the pamphlet is 1841.)

Report of Lieut.-Colonel Sir Frederic Smith, R.E., and Professor Barlow to the Rt. Hon. the Earl of Ripon, President of the Board of Trade, on the Atmospheric Railway. Presented to both Houses of Parliament by command of Her Majesty. London 1842.

Report on the Railway constructed from Kingstown to Dalkey in Ireland, upon the Atmospheric System, and upon the Application of this System to Railroads in general. By C. Mallet. Dated Paris, January 10, 1844.

Report on the Atmospheric Railway System. By Robert Stephenson, Esq. London 1844.

Croydon and Epsom Railway, &c. &c. Minutes of the Evidence of the Engineers examined before the Committee on the Croydon and Epsom and South Western and Epsom Railway Bills, with reference to the Working of Railways upon the Atmospheric Principle. Ordered by the House of Commons to be printed June 10,1844.

Report from the Select Committee on Atmospheric Railways j together with the Minutes of Evidence. Ordered by the House of Commons to be printed April 24, 1845.

Minutes of Proceedings of the Institution of Civil Engineers. London 1844 and 1845.

Railways: their Rise, Progress, and Construction, &c. By Robert Ritchie. London 1846.

Tube Propulseur, Hallette, &c. &c. Paris.

The Railway Chronicle. London 1846 to 1848.

Reports of the South Devon Railway.

Traits EMmentaire des Chemins de Per. Par Aug. Perdonnet. Paris 1860.

See Also

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