d up. In the
old-fashioned house clocks, which were wound up by merely pulling one of
the strings, and in which one such winding served for both the going and
striking parts, this was done by what is called the endless chain of
Huygens, which consists of a string or chain with the ends joined
together, and passing over two pulleys on the arbors of the great
wheels, with deep grooves and spikes in them, to prevent the chain from
slipping. In one of the two loops or festoons which hang from the upper
pulleys is a loose pulley without spikes, carrying the clock-weight, and
in the other a small weight only heavy enough to keep the chain close to
the upper pulleys. Now, suppose one of those pulleys to be on the arbor
of the great wheel of the striking part, with a ratchet and click, and
the other pulley fixed to the arbor of the great wheel of the going
part; then (whenever the clock is not striking) the weight may be pulled
up by pulling down that part of the string which hangs from the other
side of the striking part; and yet the weight will be acting on the
going part all the time. It would be just the same if the striking part
and its pulley were wound up with a key, instead of the string being
pulled, and also the same, if there were no striking part at all, but
the second pulley were put on a blank arbor, except that in that case
the weight would take twice as long to run down, supposing that the
striking part generally requires the same weight x fall as the going
part.

[Illustration: FIG. 25.--Harrison's Going-Ratchet.]

This kind of going barrel, however, is evidently not suited to the
delicacy of an astronomical clock; and Harrison's going ratchet is now
universally adopted in such clocks, and also in chronometers and watches
for keeping the action of the train on the escapement during the
winding. Fig. 25 (in which the same letters are used as in the
corresponding parts of fig. 3) shows its construction. The click of the
barrel-ratchet R is set upon another larger ratchet-wheel with its teeth
pointing the opposite way, and its click rT is set in the clock frame.
That ratchet is connected with the great wheel by a spring ss' pressing
against the two pins s in the ratchet and s' in the wheel. When the
weight is wound up (which is equivalent to taking it off), the click Tr
prevents that ratchet from turning back or to the right; and as the
spring ss' is kept by the weight in a state of tension equivalent to the
wei