eel tooth we draw the line _C d_, from the point of the
escape-wheel tooth resting on the locking stone shown at _C_ at an angle
of twenty-eight degrees to radial line _C k_. We have already discussed
how to locate and plant the center of the balance staff.

We shall not show in this drawing the angular motion of the escape
wheel, but delineate at the radial lines _c e_ and _c f_ of the arc of
the balance during the extent of its implication with the periphery of
the escape wheel, which arc is one of about forty-eight degrees. Of this
angle but forty-three degrees is attempted to be utilized for the
purpose of impulse, five degrees being allowed for the impulse jewel to
pass inside of the arc of periphery of the escape wheel before the
locking jewel releases the tooth of the escape wheel resting upon it. At
this point it is supposed the escape wheel attacks the impulse jewel,
because, as we just explained, the locking jewel has released the tooth
engaging it. Now, if the train had no weight, no inertia to overcome,
the escape wheel tooth _A^2_ would move forward and attack the impulse
pallet instantly; but, in fact, as we have already explained, there will
be an appreciable time elapse before the tooth overtakes the
rapidly-moving impulse jewel. It will, of course, be understood that the
reference letters used herein refer to the illustrations that have
appeared on preceding pages.

If we reason carefully on the matter, we will readily comprehend that we
can move the locking jewel, i.e., set it so the unlocking will take
place in reality before the impulse jewel has passed through the entire
five degrees of arc embraced between the radial lines _c e_ and _c g_,
Fig. 141, and yet have the tooth attack the jewel after the five degrees
of arc. In practice it is safe to set the discharging jewel _h_ so the
release of the held tooth _A^1_ will take place as soon as the tooth
_A^2_ is inside the principal line of the escape wheel. As we
previously explained, the contact between _A^2_ and the impulse jewel
_i_ would not in reality occur until the said jewel _i_ had fully passed
through the arc (five degrees) embraced between the radial lines _c e_
and _c g_.

At this point we will explain why we drew the front fan of the
escape-wheel teeth at the angle of twenty-eight degrees. If the fan of
impulse jewel _i_ is set radial to the axis of the balance, the
engagement of the tooth _A^2_ would be at a disadvantage if it took
pla