one and a half degrees
of lock; and by measuring down on the arc _d'_ ten degrees from its
intersection with the peripheral line _m_, we locate the point _s_,
which determines the position of the inner angle of the entrance pallet,
and we know for a certainty that when this inner angle is freed from the
tooth it will be after the pallet (and, of course, the lever) has passed
through exactly ten degrees of angular motion.

For locating the inner angle of the exit pallet, we measure on the arc
_d'_, from its intersection with the peripheral line _m_, eight and a
half degrees, and establish the point _n_, which locates the position of
this inner angle; and, of course, one and a half degrees added on the
arc _d'_ indicates the extent of the lock on this pallet. Such drawings
not only enable us to theorize to extreme exactness, but also give us
proportionate measurements, which can be carried into actual
construction.

THE CLUB-TOOTH LEVER ESCAPEMENT.

We will now take up the club-tooth form of the lever escapement. This
form of tooth has in the United States and in Switzerland almost
entirely superceded the ratchet tooth. The principal reason for its
finding so much favor is, we think, chiefly owing to the fact that this
form of tooth is better able to stand the manipulations of the
able-bodied watchmaker, who possesses more strength than skill. We will
not pause now, however, to consider the comparative merits of the
ratchet and club-tooth forms of the lever escapement, but leave this
part of the theme for discussion after we have given full instructions
for delineating both forms.

With the ratchet-tooth lever escapement all of the impulse must be
derived from the pallets, but in the club-tooth escapement we can divide
the impulse planes between the pallets and the teeth to suit our fancy;
or perhaps it would be better to say carry out theories, because we have
it in our power, in this form of the lever escapement, to indulge
ourselves in many changes of the relations of the several parts. With
the ratchet tooth the principal changes we could make would be from
pallets with equidistant lockings to circular pallets. The club-tooth
escape wheel not only allows of circular pallets and equidistant
lockings, but we can divide the impulse between the pallets and the
teeth in such a way as will carry out many theoretical advantages which,
after a full knowledge of the escapement action is acquired, will
naturally suggest