*Project Gutenberg*. Public domain.

ANGULAR MOTION OF ESCAPE WHEEL DETERMINED.

The arc (three and a half degrees) of the circle *a*
embraced between the radial lines *A b* and *A
e* determines the angular motion of the escape
wheel utilized by the escape-wheel tooth. To establish
and define the extent of angular motion of the escape
wheel utilized by the pallet, we lay off seven degrees
on the arc *a* from the point *o* and establish
the point *n*, and through the point *n*,
from *B* as a center, we sweep the short arc
*n’*. Now somewhere on this arc *n’*
will be located the inner angle of the entrance pallet.
With a carefully-made drawing, having the escape wheel
10” in diameter, it will be seen that the arc
*a* separates considerably from the line, *B
f’* where it crosses the arc *n’*.

It will be remembered that when drawing the ratchet-tooth
lever escapement a measurement of eight and a half
degrees was made on the arc *n’* down from
its intersection with the pitch circle, and thus the
inner angle of the pallet was located. In the
present instance the addendum line *w* becomes
the controlling arc, and it will be further noticed
on the large drawing that the line *B h* at its
intersection with the arc *n’* approaches
nearer to the arc *w* than does the line *B
f’* to the pitch circle *a*; consequently,
the inner angle of the pallet should not in this instance
be carried down on the arc *n’* so far to
correct the error as in the ratchet tooth.

Reason tells us that if we measure ten degrees down
on the arc *n’* from its intersection with
the addendum circle *w* we must define the position
of the inner angle of the entrance pallet. We
name the point so established the point *r*.
The outer angle of this pallet is located at the intersection
of the radial line *A b* with the line *B i*;
said intersection we name the point *v*.
Draw a line from the point *v* to the point *r*,
and we define the impulse face of the entrance pallet;
and the angular motion obtained from it as relates
to the pallet staff embraces six degrees.

Measured on the arc *l*, the entire ten degrees
of angular motion is as follows: Two and a half
degrees from the impulse face of the tooth, and indicated
between the lines *B h* and *B f*; one and
a half degrees lock between the lines *B f’*
and *B i*; six degrees impulse from pallet face,
entrance between the lines *B i* and *B j*.

A DEPARTURE FROM FORMER PRACTICES.

Grossmann and Britten, in all their delineations of the club-tooth escapement, show the exit pallet as disengaged. To vary from this beaten track we will draw our exit pallet as locked. There are other reasons which prompt us to do this, one of which is, pupils are apt to fall into a rut and only learn to do things a certain way, and that way just as they are instructed.