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.


MAKING AN ESCAPEMENT MODEL.

[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