This subject will
be taken up again when we consider double-roller action. The extent or
length of the outer face of the prong is also an open subject, but as
there is but one factor of the problem of lever escapement construction
depending on it, when we name this and see this requirement satisfied we
have made an end of this question. The function performed by the outer
face of the prong of a fork is to prevent the engaged pallet from
unlocking while the guard pin is opposite to the passing hollow.
The inner angle _s_ of the horn of the fork must be so shaped and
located that the jewel pin will just clear it as it passes out of the
fork, or when it passes into the fork in the act of unlocking the
escapement. In escapements with solid bankings a trifle is allowed, that
is, the fork is made enough shorter than the absolute theoretical length
to allow for safety in this respect.
THE PROPER LENGTH OF A LEVER.
We will now see how long a lever must be to perform its functions
perfectly.
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