perhaps greater,
inconveniences caused his invention to be speedily rejected. We shall
give our readers an idea of what Dr. Hook's escapement was like.

[Illustration: Fig. 158]

[Illustration: Fig. 159]

On looking at Fig. 156 we see the escape wheel _R_, which was flat and
in the form of a ratchet; it was provided with two balances. _B B_
engaging each other in teeth, each one carrying a pallet _P P'_ upon its
axis; the axes of the three wheels being parallel. Now, in our drawing,
the tooth _a_ of the escape wheel exerts its lift upon the pallet _P'_;
when this tooth escapes the tooth _b_ will fall upon the pallet _P'_ on
the opposite side, a recoil will be produced upon the action of the two
united balances, then the tooth _b_ will give its impulse in the
contrary direction. Considerable analogy exists between this form of
escapement and that shown in Fig. 153 and intended for clocks. This was
the busy era in the watchmaker's line. All the great heads were
pondering upon the subject and everyone was on the _qui vive_ for the
newest thing in the art.

In 1674 Huygens brought out the first watch having a regulating spring
in the form of a spiral; the merit of this invention was disputed by the
English savant, Dr. Hook, who pretended, as did Galileo, in the
application of the pendulum, to have priority in the idea. Huygens, who
had discovered and corrected the irregularities in the oscillations of
the pendulum, did not think of those of the balance with the spiral
spring. And it was not until the close of the year 1750 that Pierre Le
Roy and Ferdinand Berthoud studied the conditions of isochronism
pertaining to the spiral.

AN INVENTION THAT CREATED MUCH ENTHUSIASM.

However that may be, this magnificent invention, like the adaptation of
the pendulum, was welcomed with general enthusiasm throughout the
scientific world: without spiral and without pendulum, no other
escapement but the recoil escapement was possible; a new highway was
thus opened to the searchers. The water clocks (clepsydrae) and the hour
glasses disappeared completely, and the timepieces which had till then
only marked the hours, having been perfected up to the point of keeping
more exact time, were graced with the addition of another hand to tell
off the minutes.

[Illustration: Fig. 160]

[Illustration: Fig. 161]

It was not until 1695 that the first _dead-beat escapement_ appeared
upon the scene; during the interval of over twenty year