. Watch and clock escapements; . Fig. 153 Fig. 153 forked arm was not thought of, for the pendulum itself formed apart of the verge. A far-reaching step had been taken, but it soonbecame apparent that perfection was still a long way off. The crown-wheel escapement forcibly incited the pendulum to wider oscillations ;these oscillations not being as Galileo had believed, of unvaried dura-tions, but they varied sensibly with the intensity of the motive power. THE ATTAINMENT OF ISOCHRONISM BY HUYGENS. Huygens rendered his pendulum isochronous; that is, com-pelled it to make its oscillations of equ
. Watch and clock escapements; . Fig. 153 Fig. 153 forked arm was not thought of, for the pendulum itself formed apart of the verge. A far-reaching step had been taken, but it soonbecame apparent that perfection was still a long way off. The crown-wheel escapement forcibly incited the pendulum to wider oscillations ;these oscillations not being as Galileo had believed, of unvaried dura-tions, but they varied sensibly with the intensity of the motive power. THE ATTAINMENT OF ISOCHRONISM BY HUYGENS. Huygens rendered his pendulum isochronous; that is, com-pelled it to make its oscillations of equal duration, whatever mightbe the arc described, by suspending the pendulum between twometallic curves c c, each one formed by an arc of a cycloid andagainst which the suspending cord must lie upon each forward or i6o Watch and Clock Fig. 154 backward oscillation. We show this device in Fig. 151. In greatoscillations, and by that we mean oscillations under a greaterimpulse, the pendulum would thus be shortened and the shorteningwould correct the time of the oscillation. However, the applica-tion of an exact cycloidal arc was amatter of no little difficulty, if notan impossibility in practice, andpractical men began to grope aboutin search of an escapement whichwould permit the use of shorterarcs of oscillation. At London thehorologist, G. Clement, solved theproblem in 1675 with his rackescapement and recoil anchor. Inthe interval other means wereinvented, especially the addition ofa second pendulum to correct the irregularities of the first. Suchan escapement is pictured in Fig. 152. The verge is again verticaland carries near its upper end two arms D D, which are each con-nected by a cord with a pendulum. The two pendulums oscillate con-stantly in the inverse sense theone to the other. ANOTHER TWO-PENDULUMESCAPEM
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