rsection the point _l_. Now the end of the guard point _C_
terminates at the point _l_, and the passing hollow _E_ extends on _b_
sixteen degrees on each side of the radial line _B c_.

[Illustration: Fig. 82]

The roller action is supposed to continue through thirty degrees of
angular motion of the balance staff, and is embraced on the circle _a_
between the radial line _B k_ and _B o_. To delineate the inner face of
the horn _p_ of the fork _F_ we draw the short arc _g_, from _A_ as a
center, and on said arc locate at two degrees from the center at _B_ the
point _f_. We will designate the upper angle of the outer face of the
jewel pin _D_ as the point _s_ and, from _A_ as a center, sweep through
this point _s_ the short arc _n n_. Parallel with the line _A i_ and at
the distance of half the diameter of the jewel pin _D_, we draw the
short lines _t t'_, which define the inner faces of the fork.

The intersection of the short line _t_ with the arc _n_ we will
designate the point _r_. With our dividers set to embrace the space
between the point _r_ and the point _f_, we sweep the arc which defines
the inner face of the prong of the fork. The space we just made use of
is practically the same as the radius of the circle _a_, and
consequently of the same curvature. Practically, the length of the guard
point _C'_ is made as long as will, with certainty, clear the safety
roller _B_ in all positions. While we set the point _f_ at two degrees
from the center _B_, still, in a well-constructed escapement, one and a
half degrees should be sufficient, but the extra half degree will do no
harm. If the roller _B'_ is accurately made and the guard point _C'_
properly fitted, the fork will not have half a degree of play.

The reader will remember that in the escapement model we described we
cut down the drop to one degree, being less by half a degree than
advised by Grossmann and Saunier. We also advised only one degree of
lock. In the perfected lever escapement, which we shall describe and
give working drawings for the construction of, we shall describe a
detached lever escapement with only eight degrees fork and pallet
action, with only three-fourths of a degree drop and three-fourths of a
degree lock, which we can assure our readers is easily within the limits
of practical construction by modern machinery.

HOW THE GUARD POINT IS MADE.

[Illustration: Fig. 83]

The guard point _C'_, as shown at Fig. 82, is of extremely simp