EDUCATE THE EYE TO JUDGE OF ANGULAR AS WELL AS LINEAR EXTENT.

For illustration: It would be easy to design a lever escapement that
would have locking faces which were based on the idea of employing
neither system, but a compromise between 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