ering always to use the tangents to the primitive circle as
measuring points. We have fully explained how to draw in the draft angle
on the pallets when unlocked, and do not require to repeat it, except to
say, that most authorities draw a tangent R N to the locking circle M N,
forming in other words, the right angle R N A, then construct an angle
of 12deg. from R N. We have drawn ours in by our own method, which is
the correct one. While we here illustrate S N R at an angle of 12deg. it
is in reality _less_ than that amount; had we constructed S N at an
angle of 12deg. from R N, then the draw would be 12deg. from F B, when
the primitive circumference of the wheel is reached, but _more_ than
12deg. when the fork is against the bank.

The space between the discharging edge P and the heel of the tooth forms
the angle of drop J B I of 1 1/2deg.; the definition for drop is that it is
the freedom for wheel and pallet. This is not, strictly speaking,
perfectly correct, as, during the unlocking action there will be a
recoil of the wheel to the extent of the draft angle; the heel of the
tooth will therefore approach the edge P, and the discharging side of
the pallet approaches the tooth, as only the discharging edge moves on
the path P.

A good length for the teeth is 1/10 the diameter of the wheel, measured
from the primitive diameter and from the locking edge of the tooth.

The backs of the teeth are hollowed out so as not to interfere with the
pallets, and are given a nice form; likewise the rim and arms are drawn
in as light and as neat as possible, consistent with strength.

Having explained the delineation of the wheel and pallet action we will
now turn our attention to that of the fork and roller. We tried to
explain these actions in such a manner that by the time we came to
delineate them no difficulty would be found, as in our analysis we
discussed the subject sufficiently to enable any one of ordinary
intelligence to obtain a correct knowledge of them. The fork and roller
action in straight line, right, or any other angle is delineated after
the methods we are about to give.

We specified that the acting length of fork was to be equal to the
center distance of wheel and pallets; this gives a fork of a fair
length.

Having drawn the line of centers A' A we will construct an angle equal
to half the angular motion of the pallets; the latter in the case under
consideration being 10 1/4deg., therefore 5 1/8deg. is sp