how many
grains of force the fork exerts on the jewel pin, and also how much (or,
rather, what percentage) of the motive power is lost in various "power
leaks," like "drop" and lost motion. In the present case the mechanical
result we desire to obtain is to cause our lever pivoted at _k_ to
vibrate back and forth through an arc of eight and one-half degrees;
this lever not only to vibrate back and forth, but also to lock and hold
the escape wheel during a certain period of time; that is, through the
period of time the balance is performing its excursion and the jewel pin
free and detached from the fork.

We have spoken of paper being employed for drawings, but for very
accurate delineations we would recommend the horological student to make
drawings on a flat metal plate, after perfectly smoothing the surface
and blackening it by oxidizing.

PALLET-AND-FORK ACTION.

By adopting eight and one-half degrees pallet-and-fork action we can
utilize ten and one-half degrees of escape-wheel action. We show at _A A'_,
Fig. 9, two teeth of a ratchet-tooth escape wheel reduced one-half;
that is, the original drawing was made for an escape wheel ten inches in
diameter. We shall make a radical departure from the usual practice in
making cuts on an enlarged scale, for only such parts as we are talking
about. To explain, we show at Fig. 10 about one-half of an escape wheel
one eighth the size of our large drawing; and when we wish to show some
portion of such drawing on a larger scale we will designate such
enlargement by saying one-fourth, one-half or full size.

[Illustration: Fig. 9]

At Fig. 9 we show at half size that portion of our escapement embraced
by the dotted lines _d_, Fig. 10. This plan enables us to show very
minutely such parts as we have under consideration, and yet occupy but
little space. The arc _a_, Fig. 9, represents the periphery of the
escape wheel. On this line, ten and one-half degrees from the point of
the tooth _A_, we establish the point _c_ and draw the radial line
_c c'_. It is to be borne in mind that the arc embraced between the points
_b_ and _c_ represents the duration of contact between the tooth _A_ and
the entrance pallet of the lever. The space or short arc _c n_
represents the "drop" of the tooth.

This arc of one and one-half degrees of escape-wheel movement is a
complete loss of six and one-fourth per cent. of the entire power of the
mainspring, as brought down to the escapement; still