Illocicriz may be conveniently treated by considering (i) the nzothr, a mechanism that furnishes the impelling power whose source may be either a weight or a spring; (2) the /rain, a series of toothed wheels impelled by the motor to move pointers over a dial for the purpose of indicating the hour and its subdivisions; (3) the regulator, an arrange ment for controlling the speed of the train, so that the hour and its sub divisions may be correctly indicated (pendulum and balance-wheel, with hair-spring); (4) the escapement, which gives the impulse for the control ling oscillations of the regulator (Figure 4 represents most of the essential parts of a weight-clock: P, A, cord and drum, is the motor. The train con sists of the wheels 13, C, D, E, F, G, and the escapement of the escape wheel 11 and the anchor /{); and (5)e/cell-lc clocks, whose controlling force, either directly or indirectly, is electro-magnetism.
The are divided into three classes—namely, (t) those whose impelling power is a weight; (2) those whose impelling power is a spring; and (3) those whose impelling power is an electro-magnet. In the first class the attraction of the earth acts upon a weight suspended to a curd or a chain, and the weight, by drawing down the cord, revolves a shaft upon which the cord is wound. In the second class a contracted spiral-shaped spring by its endeavor to resume its original expanded con dition acts upon a drum and causes it to revolve. In the third class the attractive or repelling force of an electro-inagnet acts upon a piece of iron and causes it to oscillate. The first and second classes are appro priately treated together, while the third class requires a separate con sideration.
1127k/d-mo/or.—Figr,ure 4 (pl. 124) shows the arrangement of a weight motor in its simplest form. /1 is a drum on whose periphery is wound a cord (I'). The drum is fixed upon a steel shaft whose projecting front end is filed square to receive the key when the clock needs winding. The great wheel /; of the train rides loosely upon the arbor of the drum, of which the ratchet-wheel f is a part. A click (k) is screwed to the great wheel and is pressed into the teeth of the ratchet-wheel by the spring o. It is obvious that if a weight bears upon the cord P, it will turn the drum as well as the wheel 13 to the left, while if the drum is moved to the right for the purpose of winding the clock, the click will yield under the pres sure of the spring o and allow the wheel /I to remain in its position, where it is held by the next wheel of the train. It is clear that by this arrange ment the clock will have to stop during the process of winding; stoppage, however, is avoided by the maintaining power (Jig. 3) invented by John Harrison (1693-1776), which is applied on all better grades of clocks. To the above-described mechanism a second large ratchet-wheel (a) is added; the large ratchet-wheel, like the great wheel 13 (fig. 4), rides loosely upon the arbor of the drum, and is located between the small ratchet-wheel and the great wheel 13.
The click k that drops into the teeth of the small ratchet-wheel, to allow the winding of the clock, is fastened to the large ratchet-wheel; there are also fastened to the large ratchet-wheel, in two opposite posi tions, two springs (ss'), so as to press against two opposite spokes of the great wheel B; into the teeth of the ratchet-wheel a second click (C) falls loosely, and is held in this position by au arm fastened against the frame of the clock. When the weight and the cord act upon the drum, the small ratchet-wheel by means of the click (k) moves the large ratchet wheel, whose two springs (ss'), pressing against the spokes of the great wheel 11, bend and attain a certain tension. If now, when the winding
process takes place, the drum is turned to the right, the tension of the springs ss' will have the tendency to move the large ratchet-wheel to the right and the great wheel to the left. The large ratchet-wheel is pre vented from moving to the right by the click C dropping into its teeth, which, yielding under the pressure of the springs, move the train.
Spring-mo/or.--Figures 9 and ro (p1. 123) show the arrangement of a spring-motor under two different conditions, wound and unwound. It consists of a cylindrical capsule b, called a "barrel;" of a spring a, a tempered band of steel of spiral shape (pl. 123, fig. 4); and of an axis, called an "arbor," upon which the barrel loosely turns. The spring, as shown in Figure 9, is placed in the barrel, against whose inner periphery it presses tightly. One end of the spring is hooked into a projecting pin of the arbor, and the other end is hooked into a pin of the barrel. Fig ure 9 shows the spring in its expanded state in the barrel, and Figure io in its contracted state when wound up on the arbor.
There are two ways of using this arrangement as the impelling medium. If, as in Figure io, the arbor is made immovable, the barrel will follow the outer end of the expanding spring in the direction indicated by the arrow; while, if the barrel is fixed, the arbor will follow the movement of the inner end of the spring and turn in a direction opposite to that indicated by the arrow. The rotations thus produced may be transferred to the train of the time-keeper in two ways: (r) by means of a chain, one end of which is hooked to the periphery of the barrel, while the other portion of the chain is wound upon the arbor of the great wheel; and (2) by gear ing directly into the next wheel of the train, the great wheel, which may be one piece with the barrel. Of the first-named arrangement Figure 4 gives the perspective and Figure 5 the side view. When the barrel turns tinder the expansion of the spring, it will wind up the chain on its own circumference, and thereby revolve the great wheel. In Figure 5, f is the barrel, with a large portion of the chain wound up on its periph ery. The arbor a' of the barrel is held in position between two metal plates A, B by its pivots; Y is the arbor of the wheel to be moved by the chain, and bears besides the wheel the so-called "fusee," which is also held in position by the plates A, B. The fusee is a cone (s), with a groove running spirally over its surface from the smallest diameter to the greatest diameter, to which latter the chain is fastened at Y . Projecting through the plates is the fusee-arbor, a part of which is filed square to receive the winding key. If the key is turned to the right, the fusee will revolve and draw the chain from the barrel into its groove, since this turns the barrel, while its arbor remains fixed; hence the spring will be wound around the arbor. When the spring is entirely wound and has attained its greatest tension, the chain in the groove has reached the smallest diam eter of the fusee. As the spring runs down and its tension becomes less, the chain gradually unwinds toward the larger diameter of the fusee s. By this arrangement a constant power is attained, the shape of the cone being so formed that the diameter of the fusee increases in the proportion that the tension of the spring relaxes while expanding. In Figure 4, A is the barrel and spring, 13 the chain, C the fusee, and D the great wheel of the train.