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.
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