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, up to the present
time, no remedy has been devised to overcome it. All the other
escapements, including the chronometer, duplex and cylinder, are quite
as wasteful of power, if not more so. It is usual to construct
ratchet-tooth pallets so as to utilize but ten degrees of escape-wheel
action; but we shall show that half a degree more can be utilized by
adopting the eight and one-half degree fork action and employing a
double-roller safety action to prevent over-banking.

[Illustration: Fig. 10]