and rules for setting an escapement, especially
in American watches, which, if once acquired, conquers all
imperfections. Now we wish to disabuse the minds of our readers of any
such notions. Although the lever escapement, as adopted by our American
factories, is constructed on certain "lines," still these lines are
subject to modifications, such as may be demanded for certain defects of
construction. If we could duplicate every part of a watch movement
perfectly, then we could have certain rules to go by, and fixed
templets could be used for setting pallet stones and correcting other
escapement faults.

Let us now make an analysis of the action of a lever escapement. We show
at Fig. 89 an ordinary eighteen-size full-plate lever with fork and
pallets. The dotted lines _a b_ are supposed to represent an angular
movement of ten degrees. 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. We shall also cut the drop down to three-quarters
of a degree. By these two economies we more than make up for the power
lost in unlocking. With highly polished ruby or sapphire pallets ten
degrees of draw is ample. But such draw must positively be ten degrees
from a neutral locking face, not an escapement drawn on p