*Project Gutenberg*. Public domain.

We again lay off two and a half degrees from the intersection
of the line *A b* with the arc *a*, but
this time to the right of said intersection, and through
the point so established, and from *B* as a center,
we sweep the arc *e*. From the intersection
of the radial line *A g* with the arc *a*
we lay off to the left five and a half degrees on
said arc, and through the point so established draw
the radial line *A f*. With the dividers
set at five inches we sweep the short arc *m*
from *B* as a center. From the intersection
of the line *h B h’* with the arc *m*
we lay off on said arc and above the line *h’*
four and a half degrees, and through the point so
established draw the line *B j*.

We next set the dividers so they embrace the space
on the radial line *A b* 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.

Before we proceed to delineate the exit pallet of our escapement, let us reason on the relations of the several parts.