have been drawn tangent to the circle _s_, which represents the
locking angle of the teeth. This would have placed the center of the
pallet staff farther in, or closer to the wheel. Any person can see at a
glance that the pallets as delineated are not tangential in a true
sense.

[Illustration: Fig. 85]

We have previously considered engaging friction and also repeatedly have
spoken of tangential lockings, but will repeat the idea of tangential
lockings at Fig. 85. A tangential locking is neutral, or nearly so, as
regards engaging friction. For illustration we refer to Fig. 85, where
_A_ represents the center of an escape wheel. We draw the radial lines
_A y_ and _A z_ so that they embrace sixty degrees of the arcs _s_ or
_t_, which correspond to similar circles in Fig. 84, and represent the
extreme extent of the teeth and likewise the locking angle of such
teeth. In fact, with the club-tooth escapement all that part of a tooth
which extends beyond the line _s_ should be considered the same as the
addendum in gear wheels. Consequently, a tangential locking made to
coincide with the center of the impulse plane, as recommended by
Saunier, would require the pallet staff to be located at _C'_ instead of
_C_, as he draws it. If the angle _k'_ of the tooth _k_ in Fig. 84 was
extended outward from the center _A_ so it would engage or rest on the
locking face of the entrance pallet as shown at Fig. 84, then the draw
of the locking angle would not be quite fifteen degrees; but it is
evident no lock can take place until the angle _a_ of the entrance
pallet has passed inside the circle _s_. We would say here that we have
added the letters _s_ and _t_ to the original drawings, as we have
frequently to refer to these circles, and without letters had no means
of designation. Before the locking angle _k'_ of the tooth can engage
the pallet, as shown in Fig. 84, the pallet must turn on the center _C_
through an angular movement of at least four degrees. We show the
situation in the diagram at Fig. 86, using the same letters of reference
for similar parts as in Fig. 84.

[Illustration: Fig. 86]

As drawn in Fig. 84 the angle of draft _G a I_ is equal to fifteen
degrees, but when brought in a position to act as shown at _G a' I'_,
Fig. 86, the draw is less even than twelve degrees. The angle _C a I_
remains constant, as shown at _C a' I'_, but the relation to the radial
_A G_ changes when the pallet moves through the angle _w C w'_,