Now, it is the function of the fork to carry
the power of the train to the balance. How well the fork performs its
office we will consider subsequently; for the present we are dealing
with the power as conveyed to the fork by the pallets as shown at Fig.
89.
[Illustration: Fig. 89]
The angular motion between the lines _a c_ (which represents the lock)
is not only absolutely lost--wasted--but during this movement the train
has to retrograde; that is, the dynamic force stored in the momentum of
the balance has to actually turn the train backward and against the
force of the mainspring. True, it is only through a very short arc, but
the necessary force to effect this has to be discounted from the power
stored in the balance from a former impulse. For this reason we should
make the angular motion of unlocking as brief as possible. Grossmann, in
his essay, endorses one and a half degrees as the proper lock.
In the description which we employed in describing the large model for
illustrating the action of the detached lever escapement, we cut the
lock to one degree, and in the description of the up-to-date lever
escapement, which we shall hereafter give, we shall cut the lock down to
three-quarters of a degree, a perfection easily to be attained by modern
tools and appliances.
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