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[Barbella T. <co...@re...>]

G. 23.] [Illustration: Fig. 22.] English watches are met with having a cylindrical or round ruby pin. Such a pin should never be put

into a watch. The law of the parallelogram of forces is completely ignored by using such a pin; the friction during the unlocking and impulse actions is too severe, as it is, without the addition of so unmechanical an arrangement. Fig. 21 illustrates the action of a round ruby pin; _ii_ is the path of the ruby pin; _cc_ that of the acting length of the fork. It is shown at the moment the impulse is transmitted. It will be seen that the impact takes place _below_ the center of the ruby pin, whereas it should take place at the center, as the motion of the fork is _upwards_
and that of the ruby pin _downwards_ until the line of the centers has been reached. The same rule applies to the
flat-faced pin and it is important that the right quantity be ground off. We find that 3/7 is approximately the amount which should
be ground away. Fig. 22 illustrates the fork standing against the bank. The ruby pin touches the side of
the slot but has not as yet begun to act; _ri_ is the real impulse circle for which we allow 1 1/4deg. of freedom at the acting edge of the fork; the

face of the ruby pin is therefore on this
line. The next thing to do is to find the center of the pin. From the side _n_ of the slot we construct

the right angle _o n t_; from _n_, we transmit 1/2 the width of the pin, and plant the center _x_ on the line _n t_. We can have the center

of the pin slightly below this line,

but in no case above it; but if we put it below, the pin will be thinner and therefore more easily broken. [Illustration: Fig. 14.]
_The Safety Action._ Although this action is separate from the impulse and unlocking actions, it is still very

closely connected with them, much more so in the single than in the double roller
escapement. If we were to place the ruby

pin at _X_, Fig. 14, we could have a much smaller roller than by placing
it at _P_. With the small roller the safety action is m