An attempt was indeed made to snatch from Huygens and confer upon Galileo the glory of having first applied the pendulum to a clock, but this attempt not having been made until some time after the publication of “Huygens’ Memoirs,” it was impossible to place any faith in the contention.  If Galileo had indeed solved the beautiful problem, both in the conception and the fact, the honor of the discovery was lost to him by the laziness and negligence of his pupil, Viviani, upon whom he had placed such high hopes.  One thing is certain, that the right of priority of the discovery and the recognition of the entire world has been incontestably bestowed upon Huygens.  The escapement which Galileo is supposed to have conceived and to which he applied the pendulum, is shown in Fig. 149.  The wheel R is supplied with teeth, which lock against the piece D attached to a lever pivoted at a, and also with pins calculated to impart impulses to the pendulum through the pallet P.  The arm L serves to disengage or unlock the wheel by lifting the lever D upon the return oscillation of the pendulum.

[Illustration:  Fig. 152]

[Illustration:  Fig. 153]

A careful study of Fig. 150 will discover a simple transposition which it became necessary to make in the clocks, for the effectual adaptation of the pendulum to their regulation.  The verge V was set up horizontally and the pendulum B, suspended freely from a flexible cord, received the impulses through the intermediation of the forked arm F, which formed a part of the verge.  At first this forked arm was not thought of, for the pendulum itself formed a part of the verge.  A far-reaching step had been taken, but it soon became 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 durations, but they varied sensibly with the intensity of the motive power.

THE ATTAINMENT OF ISOCHRONISM BY HUYGENS.

Huygens rendered his pendulum isochronous; that is, compelled it to make its oscillations of equal duration, whatever might be the arc described, by suspending the pendulum between two metallic curves c c’, each one formed by an arc of a cycloid and against which the suspending cord must lie upon each forward or backward oscillation.  We show this device in Fig. 151.  In great oscillations, and by that we mean oscillations under a greater impulse, the pendulum would thus be shortened and the shortening would correct the time of the oscillation.  However, the application of an exact cycloidal arc was a matter of no little difficulty, if not an impossibility in practice, and practical men began to grope about in search of an escapement which would permit the use of shorter arcs of oscillation.  At London the