noying
stoppages, often characterized by the watch starting when taken from the
pocket.

The action is very important and is generally divided into impulse and
safety action, although we think we ought to divide it into three,
namely, by adding that of the unlocking action. We will first of all
consider the impulse and unlocking actions, because we cannot
intelligently consider the one without the other, as the ruby pin and
the slot in the fork are utilized in each. The ruby pin, or strictly
speaking, the "impulse radius," is a lever arm, whose length is measured
from the center of the balance staff to the face of the ruby pin, and is
used, firstly, as a power or transmitting lever on the acting or
geometrical length of the fork (_i. e._, from the pallet center to the
beginning of the horn), and which at the moment is a resistance lever,
to be utilized in unlocking the pallets. After the pallets are unlocked
the conditions are reversed, and we now find the lever fork, through the
pallets, transmitting power to the balance by means of the impulse
radius. In the first part of the action we have a short lever engaging a
longer one, which is an advantage. See Fig. 14, where we have purposely
somewhat exaggerated the conditions. A'X represents the impulse radius
at present under discussion, and AW the acting length of the fork. It
will be seen that the shorter the impulse radius, or in other words, the
closer the ruby pin is to the balance staff and the longer the fork, the
easier will the unlocking of the pallets be performed, but this entails
a great impulse angle, for the law applicable to the case is, that the
angles are in the inverse ratio to the radii. In other words, the
shorter the radius, the greater is the angle, and the smaller the angle
the greater is the radius. We know, though, that we must have as small
an impulse angle as possible in order that the balance should be highly
detached. Here is one point in favor of a short impulse radius, and one
against it. Now, let us turn to the impulse action. Here we have the
long lever AW acting on a short one, A'X, which is a disadvantage. Here,
then, we ought to try and have a short lever acting on a long one, which
would point to a short fork and a great impulse radius. Suppose AP,
Fig. 14, is the length of fork, and A'P is the impulse radius; here,
then, we favor the impulse, and it is directly in accordance with the
theory of the free vibration of the balance, for, a