process of
escaping.

When the tooth of a cylinder escape wheel while performing its
functions, strikes the cylinder shell, it rests dead on the outer or
inner surface of the half shell until the action of the balance spring
has brought the lip of the cylinder so that the impulse face of the
tooth commences to impart motion or power to the balance.

[Illustration: Fig. 122]

[Illustration: Fig. 123]

[Illustration: Fig. 124]

[Illustration: Fig. 125]

[Illustration: Fig. 126]

[Illustration: Fig. 127]

[Illustration: Fig. 128]

Most writers on horological matters term this act the "lift," which name
was no doubt acquired when escapements were chiefly confined to pendulum
clocks. Very little thought on the matter will show any person who
inspects Fig. 126 that if the tooth _C_ is released or escapes from the
inside of the half shell of the cylinder _A_, said cylinder must turn or
revolve a little in the direction of the arrow _j_, and also that the
next succeeding tooth of the escape wheel will engage the cylinder on
the outside of the half shell, falling on the dead or neutral portion of
said cylinder, to rest until the hairspring causes the cylinder to turn
in the opposite direction and permitting the tooth now resting on the
outside of the cylinder to assume the position shown on the drawing.

The first problem in our consideration of the theoretical action of the
cylinder escapement, is to arrange the parts we have described so as to
have these two movements of the escape wheel of like angular values. To
explain what we mean by this, we must premise by saying, that as our
escape wheel has fifteen teeth and we make each tooth give two impulses
in alternate directions we must arrange to have these half-tooth
movements exactly alike, or, as stated above, of equal angular values;
and also each impulse must convey the same power or force to the
balance. All escape wheels of fifteen teeth acting by half impulses must
impel the balance during twelve degrees (minus the drop) of escape-wheel
action; or, in other words, when a tooth passes out of the cylinder from
the position shown at Fig. 126, the form of the impulse face of the
tooth and the shape of the exit lip of the cylinder must be such during
twelve degrees (less the drop) of the angular motion of the escape
wheel. The entire power of such an escape wheel is devoted to giving
impulse to the balance.

The extent of angular motion of the balance during s