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. +----------------------------------------------------------------------+ | [Illustration: Rack Striking Work.] | +----------------------------------------------------------------------+