145.
[Illustration: Figs. 145 and 146]
[Illustration: Fig. 147]
Let us imagine that our drawing is in motion, then will the tooth _d_,
of the crown wheel _R_, be pushing against the pallet _P_, and just upon
the point of slipping by or escaping, while the opposite tooth _e_ is
just about to impinge upon the advancing pallet _P'_. This it does, and
will at first, through the impulse received from the tooth _d_ be forced
back by the momentum of the pallet, that is, suffer a recoil; but on the
return journey of the pallet _P'_, the tooth _e_ will then add its
impulse to the receding pallet. The tooth _e_ having thus accomplished
its mission, will now slip by and the tooth _c_ will come in lock with
the pallet _P_ and, after the manner just described for _e_, continue
the escapement. Usually these escape wheels are provided with teeth to
the number of 11, 13 or 15, and always uneven. A great advantage
possessed by this form of escapement is that it does not require any
oil, and it may be made to work even under very inferior construction.
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