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 horologist, G.
Clement, solved the problem in 1675 with his rack escapement and recoil
anchor. In the interval other means were invented, especially the
addition of a second pendulum to correct the irregularities of the
first. Such an escapement is pictured in Fig. 152. The verge is again
vertical and carries near its upper end two arms _D D_, which are each
connected by a cord with a pendulum. The two pendulums oscillate
constantly in the inverse sense the one to the other.
[Illustration: Fig. 154]
[Illustration: Fig.
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