The Regulator has for its object the controlling of the duration of the periods of interruption to which the escape-wheel is subjected while it completes one revolution, and by which the train is compelled to move only with a speed necessary to revolve the pointers, so that they shall cor rectly indicate the time. For obtaining this result the regulating force is either the gravitation of a pendulum or the elasticity of a delicate spiral shaped spring in combination with a balance-wheel, called the "balance." The oscillations of the pendulum determine the length of the intervals between the interruptions of the escape-wheel. The num ber of these oscillations in a given time depends on the length of the pen dulum; shortening it increases their number, while lengthening it makes their number less. By this means there can be produced on the escape wheel the number of interruptions necessary for the correct indication of the time by the train. The pendulum in its simplest form consists of a rod of metal or of wood bearing on its lower end a mass of metal called the " ball," and on its upper end a spring to suspend it. Pendulums of such simple construction are affected by the variations of temperature, change their length and thereby effect a change in the number of oscillations required to be made in a given time; they can, therefore, be used only on time-keepers which are not expected to keep absolutely cor rect time. A clock to be an instrument of precision must have a pendulum whose length cannot be changed by the varying temperature of the atmo sphere. To attain such a result is the object of the compensated pendulum invented by George Graham (1703-1751). The property possessed by dif ferent metals to expand differently when subjected to the same degree of heat has suggested an ingenious method of avoiding the effects of the change in temperature.
Compensated 7 (/5/. I 2 4) shows such a compensated pendulum: it consists of five iron and four brass rods, the iron rods in the Figure being shaded darker than the brass rods. The first and longest two iron rods arc fastened above and below to a horizontal bar; the lower metal bar holds two brass rods, which carry on their upper ends a third horizon tal bar which also carries a pair of brass rods. The latter are finally con nected on their upper ends by a fifth narrow bar, from the middle of which is suspended a longer iron rod which extends through the two lower hori zontal bars and carries on its end the pendulum-ball, shaped like a len:, so that the air may offer the least possible resistance to the pendulum's oscillations. If the two outer iron rods expand, they will lower the second horizontal bar, and with it the first pair of brass rods; by the expansion of the latter, however, the third bar, which bears the second pair of iron rods, will be raised, and since the expansion of brass is greater than that of iron, the third bar will be raised proportionally to a greater extent. than the sec ond bar was lowered. If in this manner we follow the action of the entire system of iron and brass rods, we shall find that the expansion of the iron rods downward will be neutralized by the expansion of the brass rods upward, which latter expansion raises the horizontal bars to which the iron rods are suspended to such an extent that the position of the pendu lum-ball will remain unaffected by the change of temperature. The exact
proportion in the length of the iron and brass rods must, of course, be deter mined by careful measurements of the material used if the object of the whole arrangement is to be realized. The pendulum is suspended by a thin metal spring (shown in the Figure), and receives from the escape ment the impulses for the continuation of its oscillations in a manner explained on p. 368.
and Balance portable time-keepers—watches, for example—the balance and hair-spring become the regulator (pl. I, 2, 3, 6). To the arbor 0, in Figure 6, are fastened a delicate spi ral-shaped spring called a " balance- " or "hair-spring," and the balance s. The outer end of the hair-spring is fastened to the stud f. (See perspec tive view, 1, U, f) The arbor 0, being pivoted and resting in bearings, is permitted to oscillate to the right and to the left. The hair-spring when at rest will keep the balance in a fixed normal position. If, however, the balance be turned away from this point, say to the right, the elasticity of the hair-spring will bring it back to, and cause it to pass beyond, its nor mal position in consequence of the inertia thus imparted; after the balance has passel its normal position, the elasticity of the hair-spring becomes a force opposing the further progress of the balance, thereby exhausting the inertia of the balance and bringing it for a moment to a standstill, when it will be forced by the accumulated tension of the hair-spring to move to the left, when the inertia received from the hair-spring again carries it beyond its normal position, and thus keeps it oscillating until the resistance of the air and the friction of the bearings of the balance bring it gradually to a complete standstill in its normal position. The number of oscillations depends upon the tension of the hair-spring, and becomes greater in number if by a given width and thickness the spring is short ened, and less if it is lengthened; thereby an easy means is given to obtain a certain number of oscillations in a fixed time.
Figure 6 shows an old arrangement for this purpose. A section of a toothed wheel a gears into a partly-toothed wheel b; a has an extension e, and is movable in the grooves a', e of the rounded metal piece a'. The extension of a bears at c two pins, between which the outer coil of the hair-spring loosely plays. If now the little pointer r of the wheel b is moved toward R, the pins at c will move to the right, and thereby lengthen the hair-spring and decrease the number of oscillations of the balance; if the pointer is moved toward A, the pins at c will move in the opposite direction and shorten the hair-spring, thereby increasing the number of oscillations.