, [Fig. 17], we illustrate such a ruby pin; the theoretical and real impulse radius coincide with one another. The intersection of the circle
ii
and
cc
is very slight, while the friction in unlocking begins within 1° of half the total movement of the fork from the line of centers; to illustrate, if the angular motion is 11° the ruby pin under discussion will begin action 4½° before the line of centers, being an engaging, or “uphill” friction of considerable magnitude.
Fig. 18.
