1851 Great Exhibition: Official Catalogue: Class X.: B. L. Vulliamy
700. VULLIAMY, B. L., 68 Pall Mall — Inventor.
Model of a peculiar method of suspending the pendulum of a large turret clock.
Model of a method not generally known of suspending a pendulum. Supposed to have been only twice reduced to practice; firstly, in the case of a clock the property of Her Majesty, and now at Osborne; secondly, in the great clock at the Post Office. The suspension of a pendulum upon the bases of four isosceles triangles is probably the best denomination for this method of suspension.
This model is made to a scale of six inches to a foot. It was proposed in this clock to employ a two-seconds pendulum, which is preferable to any other for a large clock. In the model, the length of the pendulum is regulated by the height of the stand from the floor.
The principal pieces forming this suspension are the following:—A base upon which the support rests; four supports connected together two and two; eight steel bearings; and the beam to which the pendulum is attached.
As the following description must necessarily be very brief, an attempt is made, first, to describe the construction, and then to point out a few of its advantages.
The apex of the triangles is the centre of motion; this, for the convenience of construction, is made continuous in reference to the two triangles on the same side, of which the centres of motion are in practice very small cylinders, answering the purpose of pivots, prolonged from the one to the other. The reverse ends of the four supports, though very short, are the bases of the triangles, which, when placed in their proper situation relative to each other (which is done by means of the two counterweights), form the four supports upon which the pendulum rests. The pendulum is itself immediately suspended from a beam, the underside of which terminates in a small cylinder, which in a similar manner, as in the case of the triangles, answers the purpose of two pivots. The pivots of the triangles work in sinks instead of holes, in four pieces of steel made perfectly hard, which pieces of steel are kept in their places by the pressure of the supports. The bearings upon which these four pieces rest, are arcs of circles which, should any inaccuracies occur in the execution of the work, secure for the pivots a full bearing upon the four pieces. The tops of the supports (upon which the four pieces of steel are, in which the pivots of the beam rest) are in like manner, and with the same intention, made arcs of circles; the four pieces that rest upon them, are also loose pieces made of steel and perfectly hard. By this arrangement, all inconvenience from any inaccuracy in the construction is obviated, and a full bearing given to the pivots of the beam. There is an arm attached to and projecting from the base of each of the supports, terminated by a weight. These weights act as counter-weights, to retain the supports in their proper position. The weights move upon screws, for the greater convenience of regulating their distance from the centre of motion.
The action of the parts will now be very easily explained. The pendulum being set in motion, the pivots of the beam, and the bases of the triangles upon which they bear, roll together, the friction being removed to the pivots of the triangles; but the quantity of motion is so exceedingly small that it would be very difficult to express it by a decimal fraction: it is just perceptible at the points of the arms which carry the counter-weights, and which are of the same length as the supports of the beam.
At first sight, this suspension might be considered as a modification of the well-known application of friction-rollers as supports, to a pendulum; to which mode, however, it bears no resemblance. In the case of the friction- roller, though the motion is alternately both ways, still the wheels ultimately revolve, which sufficiently proves that the motion backwards and forwards is not equal: it follows that the total circumference of the wheels must be of the same material; and as yet, no material has been discovered of sufficient hardness to make friction-rollers, when employed to support heavy weights, or which in practice did not become indented and then wear into hollows: when this commences they cease to be rollers, and friction is speedily engendered to a degree that renders them much worse than useless.
In this suspension, the case is quite different in principle and execution. The triangles which form the supports by which the pendulum is carried, have no tendency to revolve, because the places where the pivots of the beam bear (which are geometrical lines at the shortest distance from the centre of the pivots) and the eight bearings, being detached pieces, afford the convenience of being made of steel, and being perfectly hard. When the pendulum is set in motion, two of the supports ascend while two descend, moving an equal quantity each way up and down, those that ascend when the pendulum vibrates in one direction, descending when it vibrates in the other: their motion, expressed by the angle they vibrate, is determined by the arc of vibration of the pendulum. It must be specially noticed that the practical effect of this motion is to raise the beam, and consequently the pendulum, and the longer the arc of vibration, the more it is raised; but the quantity raised would with a long arc of vibration be so exceedingly small that it would be difficult to express it by a decimal fraction, consequently it is not attended with any practical inconvenience. That the pendulum must be raised is evident from the circumstance, that a line supposed to be drawn from the centre of the lower pivot to the termination of the geometrical line on the base, on which the pivot bears when the pendulum is at rest, is necessarily, from the principle of this suspension, the shortest that can be drawn between these two points. It follows that whichever way the supports move, that line must be lengthened, because the sides of an isosceles triangle, however short the base, are necessarily longer than a line that bisects into equal angles, the angle at the vertex or apex of the triangle.
There are many advantages attendant upon this mode of suspension, the principal of which may be briefly enumerated as follows:—
The power of dispensing with the pendulum spring, which renders any compensation for change of temperature in reference to the alterations in the strength of the spring caused by alteration of temperature, unnecessary, and enables a very heavy bob to be carried by a very light rod.
The omission of the crutch, by which the friction of two pivots and other inconveniences are avoided.
The facility afforded to employ a much heavier bob than can safely be suspended by a spring.
The power of giving a pendulum, with a bob of a given weight, a certain arc of vibration with much less maintaining power than would be required to produce the same arc of vibration from a similar pendulum hung by a spring; a circumstance which necessarily reduces the wear and tear of the machine.
The power of determining the exact length of the pendulum hung by a spring.
The avoidance of the whole train of evils which result from the breaking of the suspension spring, an accident which does sometimes occur, and never without great detriment to the machine.