three centuries both this crude escapement and the cruder regulator were
suffered to continue in this state without a thought of improvement;
even in 1600, when Galileo discovered the law governing the oscillation
of the pendulum, they did not suspect how important this discovery was
for the science of time measurement.

GALILEO'S EXPERIMENTS.

[Illustration: Fig. 150]

Galileo, himself, in spite of his genius for investigation, was so
engrossed in his researches that he could not seem to disengage the
simple pendulum from the compound pendulums to which he devoted his
attention; besides, he attributed to the oscillation an absolute
generality of isochronism, which they did not possess; nor did he know
how to apply his famous discovery to the measurement of time. In fact,
it was not till after more than half a century had elapsed, in 1657, to
be exact, that the celebrated Dutch mathematician and astronomer,
Huygens, published his memoirs in which he made known to the world the
degree of perfection which would accrue to clocks if the pendulum were
adopted to regulate their movement.

[Illustration: Fig. 151]

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