How much of this we can utilize in our
escapement will depend very much on the perfection and accuracy of
construction.
[Illustration: Fig. 139]
We show at Fig. 140 three teeth of an escape wheel, together with the
locking jewel _E_ and impulse jewel _D_. Now, while theoretically we
could commence the impulse as soon as the impulse jewel _D_ was inside
of the circle representing the periphery of the escape wheel, still, in
practical construction, we must allow for contingencies. Before it is
safe for the escape wheel to attack the impulse jewel, said jewel must
be safely inside of said escape wheel periphery, in order that the
attacking tooth shall act with certainty and its full effect. A good
deal of thought and study can be bestowed to great advantage on the
"action" of a chronometer escapement. Let us examine the conditions
involved. We show in Fig. 140 the impulse jewel _D_ just passing inside
the circle of the periphery of the escape wheel. Now the attendant
conditions are these: The escape wheel is locked fast and perfectly
dead, and in the effort of unlocking it has to first turn backward
against the effort of the mainspring; the power of force required for
this effort is derived from the balance in which is stored up, so to
speak, power from impulses imparted to the balance by former efforts of
the escape wheel.
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