We set our dividers to the same radius by which we sweep the arc
_i_ and set one leg at the point _b_ for a center and sweep the arc
_j'_. If we measure this arc from the point _j'_ to intersection of said
arc _j'_ with the line _l_ we will find it to be sixty-four degrees,
which accounts for our taking this number of degrees when we defined the
face of our escape-wheel tooth, Fig. 129.
There is no reason why we should take twenty-degrees for the angle _k e
l_ except that the practical construction of the larger sizes of
cylinder watches has established the fact that this is about the right
angle to employ, while in smaller watches it frequently runs up as high
as twenty-five. Although the cylinder is seemingly a very simple
escapement, it is really a very abstruce one to follow out so as to
become familiar with all of its actions.
THE CYLINDER PROPER CONSIDERED.
[Illustration: Fig. 131]
We will now proceed and consider the cylinder proper, and to aid us in
understanding the position and relation of the parts we refer to Fig.
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