Old Balance-Clock.
Without entering into any very minute detail of the manner in which motion in a clock is successively communicated from one toothed wheel (G or R) or pinion (e or g) to another, which, indeed, would only tend to perplex the mind of the general reader, it will be sufficient to state the following. S is a square piece of steel fixed to and forming part of the pinion P. In winding the clock the key is placed upon this square, and being turned round continuously in one direction, the pinion P turns with it. This communicates its motion to the wheel R, which is fixed to the cylinder B, and which in its revolution coils or winds up the cord to which is attached the weight A. While this takes place the wheel G is held in check by another wheel, called the 'ratchet,' and a click (neither of which is seen in the sketch), but when the operation of the winding is completed, and the weight A begins to descend, the cylinder B, together with the wheel G, turn on their common pivots V, V, and the motion is thus communicated from wheel to pinion until it reaches the escapement-wheel I. The teeth of this wheel, in its revolution, act alternately on the pallets i, h, which project from and form part of the spindle or verge K, M, and thus produce a vibratory or backward and forward motion of the balance L, L.
Were it not for this detention, the duration of which is much increased by the swing of the balance, the weight A would descend with gradually accelerated speed, till, in a few moments, the cord would be entirely unwound from the cylinder, and the clock be at rest.
Clock Spring.
The Spring Clock as ordinarily made is thus constructed. The frame consists of two oblong plates of brass pinned together by short pillars, and pierced with holes, in which run the arbors of the various wheels. Next, the mainspring, the moving or motive power of the clock, which is a riband of steel, highly tempered, and enclosed in a cylinder or barrel. In the middle of this barrel is the spring or barrel arbor, to which the spring is hooked at one end, the other end being fixed to the circumference of the barrel. Outside the frame or plate, and at the end of the arbor, is the ratchet, a wheel with saw-like teeth. This is acted upon by a click, which, falling into the ratchet teeth, prevents the recoil of the mainspring, so that the spring has no means of uncoiling itself, except by the moving of the train of wheels. This click is screwed to the outside of the oblong plate. The power of the mainspring is transmitted to the train of wheels by means of a chain or gut, one end of which is fastened to the outer edge of the barrel, and the other end to the fusee, which is of conical shape, securely fastened to the arbor or axis of the main wheel; on this same arbor is the square, on which the key is put for winding. When this square is turned in winding, the fusee draws the chain or gut from off the outer edge of the barrel, and coils up the spring within it. The spring when fully wound, and consequently at its greatest power, acts by means of the chain or gut on the small end of the fusee, which in turning drives the train of wheels. As the spring becomes gradually uncoiled, and the power exerted less, the leverage is increased in the same proportion by the increased width of the fusee on which it acts.
To prevent the straining of the spring, a little contrivance called the stop-work is introduced. It consists of a piece of steel somewhat in the shape of a bayonet, which is so fixed and contrived that the last turn of the gut or chain on the fusee forces the stop into contact with a projection on the end of the fusee, which abutting against it, forms the check felt when the clock is wound up. On the same arbor with the fusee is fixed the main wheel, which with the before-described contrivance of click and ratchet, permits the turning of the fusee or winding-up of the clock, while it itself remains stationary. This wheel acts in the centre pinion (a pinion is a little wheel playing in the teeth of a larger wheel, and has six, eight, ten, or twelve teeth, or, as they are called, leaves), which is fixed to the centre arbor, and carries the minute hand. This pinion is so constructed in relation to the other parts of the clock as to make one revolution in an hour; the centre wheel being firmly riveted on the pinion, it must also revolve once an hour. The centre wheel acts into another pinion, which is called the third wheel pinion, upon the arbor or axle of which is securely fixed the third wheel, which again acts in the escape-pinion carrying the escapement-wheel. On the top of the back plate is firmly screwed the back cock, or the support of the pendulum, which is suspended from it by a flexible spring, as before described. This pendulum receives impulsion from the wheel-work by means of the crutch, a small part attached to the arbor of the pallets, and which projects downwards about three inches, parallel with the pendulum rod. To the lower part of the crutch is screwed or riveted at a right angle a piece of steel, in such a direction as to penetrate the pendulum rod, which has a slot or hole cut to receive it; impulsion is thus given to the pendulum. Between the frame and dial-plate is the motion work, consisting of three wheels; the first, called the minute wheel, is attached to the arbor of the centre wheel, which, it will be recollected, makes one revolution an hour, and acts in a wheel of the same size, whose axle carries a pinion serving to drive the hour wheel. This hour wheel is supported by a bridge screwed over the minute wheel. The dial is pinned on to the front plate; the hour hand is fixed on a socket communicating with the hour wheel, and the minute hand on the arbor of the centre wheel.
When a clock is intended to strike, a separate train of wheels has to be introduced into it,—one train of wheels serving to keep the time, and another train for the striking part. It may be as well to add that a greater amount of labour is required to make the striking than the going part of a clock.
There are only two kinds of striking parts now in use, and these are characterized by the terms 'Rack' striking work, and 'Count-wheel,' or 'Locking-plate,' striking work. The Rack striking work (see next page) is the best and safest ever introduced, because with it the clock may be made to strike any number of times within the hour. A, the minute wheel