een the two, and still give a good,
sound action. All workmen should learn to estimate accurately the extent
of angular motion, so as to be able to judge correctly of escapement
actions. It is not only necessary to know that a club-tooth escapement
should have one and one-half degrees drop, but the eye should be
educated, so to speak, as to be able to judge of angular as well as
linear extent.

[Illustration: Fig. 53]

Most mechanics will estimate the size of any object measured in inches
or parts of inches very closely; but as regards angular extent, except
in a few instances, we will find mechanics but indifferent judges. To
illustrate, let us refer to Fig. 53. Here we have the base line _A A'_
and the perpendicular line _a B_. Now almost any person would be able to
see if the angle _A a B_ was equal to _B a A'_; but not five in one
hundred practical mechanics would be able to estimate with even
tolerable accuracy the measure the angles made to the base by the lines
_b c d_; and still watchmakers are required in the daily practice of
their craft to work to angular motions and movements almost as important
as to results as diameters.

What is the use of our knowing that in theory an escape-wheel tooth
should have one and one-half degrees drop, when in reality it has three
degrees? It is only by educating the eye from carefully-made drawings;
or, what is better, constructing a model on a large scale, that we can
learn to judge of proper proportion and relation of parts, especially as
we have no convenient tool for measuring the angular motion of the fork
or escape wheel. Nor is it important that we should have, if the workman
is thoroughly "booked up" in the principles involved.

As we explained early in this treatise, there is no imperative necessity
compelling us to have the pallets and fork move through ten degrees any
more than nine and one-half degrees, except that experience has proven
that ten degrees is about the right thing for good results. In this day,
when such a large percentage of lever escapements have exposed pallets,
we can very readily manipulate the pallets to match the fork and roller
action. For that matter, in many instances, with a faulty lever
escapement, the best way to go about putting it to rights is to first
set the fork and roller so they act correctly, and then bring the
pallets to conform to the angular motion of the fork so adjusted.

FORK AND ROLLER ACTION.

Although we could sa