lock at all, but would strike the pallet on the impulse instead of on
the locking face. Again, such a change might cause the jewel pin to
strike the horn of the fork, as indicated at the dotted line _m_, Fig.
99.

Dealing with such and similar abstractions by mental process requires
the closest kind of reasoning; and if we attempt to delineate all the
complications which follow even such a small change, we will find the
job a lengthy one. But with a large model having adjustable parts we
provide ourselves with the means for the very best practical solution,
and the workman who makes and manipulates such a model will soon master
the lever escapement.

QUIZ PROBLEMS IN THE DETACHED LEVER ESCAPEMENT.

Some years ago a young watchmaker friend of the writer made, at his
suggestion, a model of the lever escapement similar to the one
described, which he used to "play with," as he termed it--that is, he
would set the fork and pallets (which were adjustable) in all sorts of
ways, right ways and wrong ways, so he could watch the results. A
favorite pastime was to set every part for the best results, which was
determined by the arc of vibration of the balance. By this sort of
training he soon reached that degree of proficiency where one could no
more puzzle him with a bad lever escapement than you could spoil a meal
for him by disarranging his knife, fork and spoon.

Let us, as a practical example, take up the consideration of a short
fork. To represent this in our model we take a lever as shown at Fig.
99, with the elongated slot for the pallet staff at _g_. To facilitate
the description we reproduce at Fig. 102 the figure just mentioned, and
also employ the same letters of reference. We fancy everybody who has
any knowledge of the lever escapement has an idea of exactly what a
"short fork" is, and at the same time it would perhaps puzzle them a
good deal to explain the difference between a short fork and a roller
too small.

[Illustration: Fig. 102]

[Illustration: Fig. 103]

In our practical problems, as solved on a large escapement model, say we
first fit our fork of the proper length, and then by the slot _g_ move
the lever back a little, leaving the bankings precisely as they were.
What are the consequences of this slight change? One of the first
results which would display itself would be discovered by the guard pin
failing to perform its proper functions. For instance, the guard pin
pushed inward against the r