f shell has had too much cut away, so the tooth on entering the
half shell after parting with the entrance lip does not strike dead on
the inside of the shell, but encounters the edge of the exit lip. In
this case the impulse of the balance would cause the tooth to slightly
retrograde and the watch would go but would lack a good motion. In such
an instance a very slight advance of the chariot would remedy the
fault--not perfectly remedy it, but patch up, so to speak--and the watch
would run.

[Illustration: Fig. 135]

In this day, fine cylinder watches are not made, and only the common
kind are met with, and for this reason the student should familiarize
himself with all the imaginary faults which could occur from bad
construction. The best way to do this is to delineate what he (the
student) knows to be a faulty escapement, as, for instance, a cylinder
in which too much of the half shell is cut away; but in every instance
let the tooth be of the correct form. Then delineate an escapement in
which the cylinder is correct but the teeth faulty; also change the
thickness of the cylinder shell, so as to make the teeth too short. This
sort of practice makes the pupil think and study and he will acquire a
knowledge which will never be forgotten, but always be present to aid
him in the puzzles to which the practical watchmaker is every day
subject.

The ability to solve these perplexing problems determines in a great
degree the worth of a man to his employer, in addition to establishing
his reputation as a skilled workman. The question is frequently asked,
"How can I profitably employ myself in spare time?" It would seem that a
watchmaker could do no better than to carefully study matters
horological, striving constantly to attain a greater degree of
perfection, for by so doing his earning capacity will undoubtedly be
increased.

CHAPTER III.

THE CHRONOMETER ESCAPEMENT.

Undoubtedly "the detent," or, as it is usually termed, "the chronometer
escapement," is the most perfect of any of our portable time measurers.
Although the marine chronometer is in a sense a portable timepiece,
still it is not, like a pocket watch, capable of being adjusted to
positions. As we are all aware, the detent escapement is used in fine
pocket watches, still the general feeling of manufacturers is not
favorable to it. Much of this feeling no doubt is owing to the
mechanical difficulties presented in repairing the chronometer
escapem