between its intersection with the line _B j_ and the center _A_, and
from _A_ as a center sweep the arc _i_, said arc defining the _addendum_
of the escape-wheel teeth. We draw a line from the intersection of the
radial line _A f_ with the arc _i_ to the intersection of the radial
line _A g_ with the arc _a_, and thus define the impulse face of the
escape-wheel tooth _D_. For defining the locking face of the tooth we
draw a line at an angle of twenty-four degrees to the line _A g_, as
previously described. The back of the tooth is defined with a curve
swept from some point on the addendum circle _i_, such as our judgment
will dictate.

In the drawing shown at Fig. 20 the radius of this curve was obtained by
taking eleven and a half degrees from the degree arc of 5" radius in the
dividers, and setting one leg at the intersection of the radial line _A f_
with the arc _i_, and placing the other on the line _i_, and allowing
the point so established to serve as a center, the arc was swept for the
back of the tooth, the small circle at _n_ denoting one of the centers
just described. The length for the face of the tooth was obtained by
taking eleven degrees from the degree arc just referred to and laying
that space off on the line _p_, which defined the face of the tooth. The
line _B k_ is laid off one and a half degrees below _B h_ on the arc
_m_. The extent of this arc on the arc _d_ defines the locking face of
the entrance pallet. We set off four degrees on the arc _m_ below the
line _B k_, and through the point so established draw the line _B l_. We
draw a line from the intersection of the line _A g_ with the line _c h_
to the intersection of the arc _e_ with the line _c l_, and define the
impulse face of the entrance pallet.


RELATIONS OF THE SEVERAL PARTS.