1851 Great Exhibition: Official Catalogue: Class X.: George Dollond
145. DOLLOND, GEORGE, St. Paul's Churchyard — Inventor.
Atmospheric recorder. This instrument self-registers simultaneously, on paper, the varying pressures of the atmosphere, the changes of the temperature of air and evaporation, and those of the electrical states of the atmosphere, the fall of rain, the amount of water evaporated from a surface of water, and the force and direction of the wind.
[Self-registering instruments, which move equally by clock-work or otherwise, and are made subservient to the registration of natural phenomena, are of the highest importance, and particularly so in meteorological investigations, where the changes of every element of research are perpetual, and those which accrue during the night are of equal importance to those happening during the day.-J. G.]
The atmospheric recorder will correctly register the slightest change which takes place during any period of time, according to the length of the paper.
The apparatus is composed of a frame of about two feet by three feet six inches, firmly supported upon four pillars, the sides of the frame being strongly bolted together at two feet from each other. At one-fourth from each end of the frame, a roller of one foot in circumference is introduced. To one of these rollers an eight-day clock is attached, which moves it round once in twenty-four hours. At half right angles above that roller is another of the same dimensions, so arranged as to press upon it equally throughout its length. The last-mentioned roller is for the purpose of keeping the paper in contact with the driving or clock roller.
The apparatus is represented in the annexed Plate 95.
The roller at the other end of the frame acts as a rest for carrying the paper to be registered to a platform in the middle of the frame, which has its face in the same plane as the upper sides of the rollers.
Near the end of the frame, which is placed towards the north, is a strong bar, upon which all the fulcrums of the indicators or markers are placed, from which arms of one foot in length, having spring points at their ends for the barometer, thermometer, and hygrometer, are struck into the paper every half hour by a falling lever or frame. For the electrometer, rain, evaporator, force and direction of the wind, ever-pointed pencils are used, which make a continuous mark upon the paper, with a weight pressing upon them so as to render the marks perfectly distinct without interrupting their proper motion.
Beyond the fulcrums there are continuations of the arms of the indicators, to which are applied, by various contrivances, the powers which give motion to the indicators, in those proportions which are required by the scales of the eight instruments which mark the various changes of the atmosphere. Each indicator has its proper scale placed near to the line of the registering points and pencils, so that the last indentures or marks on the paper may be compared with their respective scales, and the time referred to at which the indication took place.
There are also a set of liners which separate each department, and form zeros or boundary lines throughout the whole run of the paper, commencing at the point or place of the indicators, from which any movement or hygrometric change of the paper may be referred to for correction.
On each side of the frame, there is a marker for time; these are governed by a wheel attached to the clock roller, which, by a lever and inclined planes, are made to register the time correctly at every half-hour, and sixth hour more strongly, for the convenience of counting. The advantage of thus marking the time on both the edges of the paper is very considerable; for when the paper is taken off, or at any time examined, a line drawn across, corresponding with the opposite marks, will show the correct period at which any change in the atmosphere took place.
Having described the general formation of the apparatus, it will be requisite to give a detailed account of those parts which are more immediately acted upon by the atmosphere, and the manner in which they are made to register the results.
The barometer is upon the siphon principle of a large bore. Upon the surface of the mercury, in the shortest leg, is placed a float very accurately counterpoised, leaving only sufficient weight to compel it to follow the mercury, and correctly adjusted to that part of the apparatus which moves the indicator, when the pressure of the atmosphere is at thirty inches. The connection of the float with the indicator is so arranged as to give a scale of three to one, which has been found to maintain the register in the most perfect manner, under comparison with an excellent instrument of the best construction.
The thermometrical arrangement consists of ten mercurial thermometers of a peculiar form. These are suspended upon an extremely delicate and accurate balance, by which a correct register of all the various changes in this climate have been found to agree with the best thermometers of the usual construction. They are placed at the north end of the frame, and are screened from the effects of the wind and rain by perforated plates of zinc.
The hygrometer consists of a slip of mahogany cut across the grain. This was placed in a cylinder filled with water, and suspended from the upper end, with a weight of two pounds at the other end, until it was found by repeated examination to be completely saturated, and no longer to increase in length. The length was then referred to an accurate scale, and the slip of mahogany placed by the side of the pipe of a stove, under the same suspension and weight, until its shortest length was obtained. The difference of the two results being carefully taken, the scale was formed accordingly. It is placed in a tube, open at both ends for a free passage of air, outside the observatory. It is suspended, and weighted as before, with full power to act upon the arm of the indicator, quite free from the action of the sun or rain, and is found to be extremely active and firm in its operation, showing upon an open scale every hundredth of its extremes in dryness and moisture. (This method of constructing a hygrometer was recommended by Henry Lawson, Esq., F. R.5., from one in his possession made for and used by the late Dr. Benjamin Franklin, which now performs with precision, although made more than half a century ago.)
The next part of the arrangement to be described is the electrometer for thunder-storms and electric changes. This is constructed by placing a well-insulated conductor upon the highest convenient place, from which a wire is brought down to an insulation on the top of the observatory, and from thence to a standard through another insulation to a metal disc, between which and a spring there is a moveable disc attached to a glass or insulating arm, for
the purpose of connecting it with an accurate support upon which it can move with the greatest facility. In connection with this arm and disc, there is a pencil carried forward to the line of indication. The spring before stated is fixed to a standard at about three inches from the first disc; to this a wire is attached and carried into the earth. By this arrangement, the electricity put in motion by a thunder-cloud is received and registered. The effect of this arrangement during a thunderstorm is extremely interesting. When a cloud charged with the electric fluid comes within the range of the conductor, the moveable disc begins slowly to pass from the first disc to the spring, discharging each time a proportion of the electricity, and increasing in rapidity of motion until the discharge of the cloud by lightning takes place. It then falls back to the first disc, and remains perfectly quiet until the next electric cloud approaches. If, in the interim, a cloud charged with rain only should descend or pass over, no movement of the disc takes place.
The pluvioineter, or that part of the apparatus which is arranged for registering the quantity of rain that falls, is formed in the following manner:—On the top of the observatory, there is a receiver of one foot square, clear from all surrounding matter that might interfere with the direct fall of the rain upon its surface. From this receiver a pipe conducts the rain into another receiver inside the observatory, directly under the registering apparatus; in this there is an air-float, connected with a set of inclined planes, each inclined plane being equal to one inch of rain. These inclined planes, as they pass up, move the indicator across the destined proportion of the paper; showing, as it proceeds, the result of each drop to the hundredth part of an inch in superficies, and continues to advance until it arrives at one inch. It is then instantly discharged, and returns to the zero of the scale, or commencement of another inch. The internal receiver is calculated to contain six inches of rain, a quantity that seldom falls in this island during one month. The register will show when it is nearly full. The water can then be drawn off without the slightest inconvenience, and the float be re-adjusted to the zero of the first inch.
The evaporator, 10, is an open cube of one foot square, which is supplied with water from the larger vessel, and is connected with the cube by a pipe underneath the two vessels, 10-10. From that connection, the indicator of evaporation is carrried to the marker or arm, 6, of the registering paper, and is supported by a float from the surface of the water in the larger vessel. The cube or evaporator is covered by a plate of glass at an angle of sufficient elevation to prevent rain from falling into it, but not so close as to resist the air from freely acting upon the surface of the water. When the water is exhausted, it may be refilled from the pump in the observatory.
The power or force of the wind is registered by a combination of suspended weights, acted upon by inclined planes or edges, in connection with a board of one foot square to receive the impression; this board is kept in opposition to the direction of the wind by a powerful vane, its motion being as free from friction as possible, every part being correctly counterpoised. When the board is acted upon by the wind, it raises the suspended weights by a chain passing over a pulley in a line with the direction of the wind, and well secured from the weather. The suspended weights in connection with an inclined lever carry the pencil of indication along the scale, which registers the weight lifted in ozs. and lbs. avoirdupois; the scale having been found, by repeated trials, to be correctly equal to the weights recorded upon it.
The direction of the wind is also registered at the same time by another pencil, which marks the course upon the paper, throughout the whole circle of the horizon, or that proportion through which it passes.
For the convenience of placing upon the instrument the paper to be registered, there is a roller, with a flange at each end, to keep it from being deranged as it is unrolled, for which proper receptacles are provided for the pivots underneath the frame, and parallel to the rollers above.
The end of the paper is carried from this roller over the one above, at the north end of the frame, and conducted under the indicators, and over the platform to the driving and pressing rollers; it is then to be drawn forward until it reaches a similar roller to that on which it was first rolled, also underneath the frame; to this roller, it is then to be fastened by springs prepared for that purpose. This roller has attached to one of its pivots a worm, upon which a weight is wound up; which weight is equal to the power requisite to wind up the paper as it comes from the driving roller, leaving a space between them, which gives the observer an opportunity of seeing what has been registered during the last twenty-four hours.
For the purpose of reading off the register when removed from the apparatus, there are a set of scales in combination, corresponding correctly with those upon the instrument.
The whole may be placed in a room six feet square, having an opening to the north for the convenience of placing the thermometer out of the range of the sun's rays, and the better for the action of the hygrometer. For the convenience of the lightning conductor and vane, an upper room would be preferable.
Lawson's meteorological thermometer stand: this apparatus consists of a frame of white deal boards, and can be formed or constructed by any carpenter. It is made of an oblong trunk 12 inches by 8 inches outside measure; to the opposite sides of which trunk are nailed boards, at the distance of three quarters of an inch, and projecting about six inches from the trunk towards the north. Outside of these are nailed other thin boards full half an inch distant, and projecting about four inches beyond the last-mentioned boards, also towards the north. These sides or shades being multiple, prevent the sun from heating the interior of the stand where the thermometers are placed. The top, or pent board, is made double, and the boards are placed at full three-quarters of an inch distant from each other, and come so forward as to overhang, by a full inch, the night index thermometer, placed immediately beneath, for the purpose of preventing rain or dew from falling perpendicularly upon the bulb of the thermometer. The legs of the stand are merely the continuation of the sides of the trunk. The board is loaded or the feet fixed to the ground, to sustain the force of the wind. The interior is blackened to prevent strong reflections of light.
The whole is to be painted white, and no other colour; except the face of the trunk, which may be black, to prevent strong reflections of light.
On the north side of the stand is an index thermometer, to give the greatest heat of the air in the shade each day; and an index spirit thermometer, to give the greatest cold of the night. There are also two thermometers, with finely-graduated scales, which are called the wet and dry bulb thermometer, to show the power of air to evaporate water, and a conical vase of considerable size to hold water for the wet bulb thermometer; it is of glass, for the purpose of seeing when it requires re-filling, and conical, to prevent its being, broken by frost.
On the south side of the stand is an index mercurial thermometer, with a black bulb, to give the greatest solar heat of each day. On this side is a rain gauge, which conveys the rain into a bottle enclosed within the trunk. From the bottle, the water is to be poured into gauge tubes, provided for the purpose of showing the quantity of rain that has fallen.
The meteorological thermometer stand, as above arranged, will be found to possess the following advantages. It can be placed in any eligible spot that may suit the convenience of its owner. Its four sides can, and must, be placed to face the cardinal points, commanding therefore a true north and south aspect. It can be visited on every side, and be free from all surrounding objects. The instruments or thermometers used, can be read off with the greatest facility; and the whole will be at a known distance from the ground. Those instruments placed on the south face, will have the meridian sun; and those on the north face, will be always in the shade, in consequence of the projecting wings. It can be employed by any meteorologist, wherever residing. It is of a determinate form, height, and size. It is not costly but firm; and can be placed on any open spot that may be thought eligible for its use. The instruments may be read off with the greatest promptitude, so as to prevent or reduce errors arising from the person of the observer being too long in the vicinity of the thermometers. By the general adoption of this stand, instruments placed upon it will all be used or observed, under similar circumstances; and deductions there from be more correctly drawn than at present. It follows, therefore, that observations made by individuals wherever residing, either in Europe, Asia, Africa, or America, if drawn from instruments thus similarly placed, can be compared one with the other with far less chance of error than has hitherto been the case.
In using instruments a certain adroitness is necessary; but a little practice will render the use of the thermometer stand in every respect easy. The thermometers used should have their bulbs perfectly free from the scales, whether of metal or wood, and that a space of at least half an inch be interposed between the bulb of each thermometer and its scale, and place whereon it is fixed; as in some states of the atmosphere, great errors will be the consequence of their touching any surrounding body. The metallic indices, in the tubes of registering thermometers are apt to tarnish and cease to slide with the required ease, which may be prevented by passing them up and down the tube, half a dozen times, at every notation of the thermometer. When the thermometers are put by, and out of use, the indexes should be moved to the end of the tube furthest from the bulb, and left there.
References to Plate 95.- 1. Barometer. 2. Thermometer. 3. Hygrometer. 4. Electrometer. 5. Pluviometer. 6. Evaporator. 7. Force of the wind. 8. Direction of the wind. 9. The Clock. 10. Receivers for Pluviometer and Evaporator.