he pallet locked; and
to delineate the pallet after five degrees of angular motion, we have
only to conceive that we substitute the line _s'_ for the line _b'_. All
angular motions and measurements for pallet actions are from the center
of the pallet staff at _B_. As we desire to now delineate the entrance
pallet, it has passed through five degrees of angular motion and the
inner angle _s_ now lies on the pitch circle of the escape wheel, the
angular space between the lines _b' s'_ being five degrees, the line
_b''_ reducing the impulse face to four degrees.

DRAWING AN ESCAPEMENT TO SHOW ANGULAR MOTION.

To delineate our locking face we draw a line at right angles to the line
_B b''_ from the point _t_, said point being located at the intersection
of the arc _o_ with the line _B b''_. To draw a line perpendicular to
_B b''_ from the point _t_, we take a convenient space in our dividers and
establish on the line _B b''_ the points _x x'_ at equal distances from
the point _t_. We open the dividers a little (no special distance) and
sweep the short arcs _x'' x'''_, as shown at Fig. 91. Through the
intersection of the short arcs _x'' x'''_ and to the point _t_ we draw
the line _t y_. The reader will see from our former explanations that
the line _t y_ represents the neutral plane of the locking face, and
that to have the proper draw we must delineate the locking face of our
pallet at twelve degrees. To do this we draw the line _t x'_ at twelve
degrees to the line _t y_, and proceed to outline our pallet faces as
shown. We can now understand, after a moment's thought, that we can
delineate the impulse face of a tooth at any point or place we choose by
laying off six degrees on the arc _m_, and drawing radial lines from _A_
to embrace such arc. To illustrate, suppose we draw the radial lines
_w' w''_ to embrace six degrees on the arc _a_. We make these lines
contiguous to the entrance pallet _C_ for convenience only. To delineate
the impulse face of the tooth, we draw a line extending from the
intersection of the radial line _A' w'_ with the arc _m_ to the
intersection of the arc _a_ with the radial line _A w''_.

[Illustration: Fig. 91]

We next desire to know where contact will take place between the
wheel-tooth _D_ and pallet _C_. To determine this we sweep, with our
dividers set so one leg rests at the escape-wheel center _A_ and the
other at the outer angle _t_ of the entrance pallet, the short arc _t' w_.
Where t