*Project Gutenberg*. Public domain.

[Illustration: Fig. 23]

From the intersection of the line *B e* with
the arc *i* we lay off two and a half degrees
on said arc, and through the point so established we
draw the line *B g*. The intersection of
this line with the arc *k* we name the point
*z*. With one leg of our dividers set at
*A* we sweep the arc *l* so it passes through
the point *z*. This last arc defines the
addendum of the escape-wheel teeth. From the point
*r* on the arc *a* we lay off three and
a half degrees, and through the point so established
draw the line *A j*.

LOCATING THE OUTER ANGLE OF THE IMPULSE PLANES.

The intersection of this line with the addendum arc
*l* locates the outer angle of the impulse planes
of the teeth, and we name it the point *x*.
From the point *r* we lay off on the arc *a*
seven degrees and establish the point *v*, which
defines the extent of the angular motion of the escape
wheel utilized by pallet. Through the point *v*,
from *B* as a center, we sweep the short arc
*m*. It will be evident on a moment’s
reflection that this arc *m* must represent the
path of movement of the outer angle of the exit pallet,
and if we measure down ten degrees from the intersection
of the arc *l* with the arc *m*, the point
so established (which we name the point *s*) must
be the exact position of the outer angle of the pallet
during locking. We have a measure of ten degrees
on the arc *m*, between the lines *B g* and
*B h*, and by taking this space in the dividers
and setting one leg at the intersection of the arc
*l* with the arc *m*, and measuring down
on *m*, we establish the point *s*.
Drawing a line from point *n* to point *s*
we define the impulse face of the pallet.

[Illustration: Fig. 24]

It is next proposed we apply the theories we have
been considering and make an enlarged model of an
escapement, as shown at Figs. 24 and 25. This
model is supposed to have an escape wheel one-fifth
the size of the 10” one we have been drawing.
In the accompanying cuts are shown only the main plate
and bridges in full lines, while the positions of the
escape wheel and balance are indicated by the dotted
circles *I B*. The cuts are to no precise
scale, but were reduced from a full-size drawing for
convenience in printing. We shall give exact dimensions,
however, so there will be no difficulty in carrying
out our instructions in construction.

[Illustration: Fig. 25]