oller would cause the engaged tooth to pass
off the locking face of the pallet, and the fork, instead of returning
against the banking, would cause the guard pin to "ride the roller"
during the entire excursion of the jewel pin. This fault produces a
scraping sound in a watch. Suppose we attempt to remedy the fault by
bending forward the guard pin _b_, as indicated by the dotted outline
_b'_ in Fig. 103, said figure being a side view of Fig. 102 seen in the
direction of the arrow _a_. This policy would prevent the engaged pallet
from passing off of the locking face of the pallet, but would be
followed by the jewel pin not passing fully into the fork, but striking
the inside face of the prong of the fork at about the point indicated by
the dotted line _m_. We can see that if the prong of the fork was
extended to about the length indicated by the outline at _c_, the action
would be as it should be.

To practically investigate this matter to the best advantage, we need
some arrangement by which we can determine the angular motion of the
lever and also of the roller and escape wheel. To do this, we provide
ourselves with a device which has already been described, but of smaller
size, for measuring fork and pallet action. The device to which we
allude is shown at Figs. 104, 105 and 106. Fig. 104 shows only the index
hand, which is made of steel about 1/20" thick and shaped as shown. The
jaws _B''_ are intended to grasp the pallet staff by the notches _e_,
and hold by friction. The prongs _l l_ are only to guard the staff so it
will readily enter the notch _e_. The circle _d_ is only to enable us to
better hold the hand _B_ flat.

[Illustration: Fig. 104]

HOW TO MEASURE ESCAPEMENT ANGLES.

From the center of the notches _e_ to the tip of the index hand _B'_ the
length is 2". This distance is also the radius of the index arc _C_.
This index arc is divided into thirty degrees, with three or four
supplementary degrees on each side, as shown. For measuring pallet
action we only require ten degrees, and for roller action thirty
degrees. The arc _C_, Fig. 105, can be made of brass and is about 11/2"
long by 1/4" wide; said arc is mounted on a brass wire about 1/8"
diameter, as shown at _k_, Fig. 106, which is a view of Fig. 105 seen in
the direction of the arrow _i_. This wire _k_ enters a base shown at
_D E_, Fig. 106, which is provided with a set-screw at _j_ for holding
the index arc at the proper height to coincide with