Instruments might also be contrived to determine the average
force of traction of horses--of the wind--of a stream or of any
irregular and fluctuating effort of animal or other natural
force.
74. Clocks and watches may be considered as instruments for
registering the number of vibrations performed by a pendulum or a
balance. The mechanism by which these numbers are counted is
technically called a scapement. It is not easy to describe: but
the various contrivances which have been adopted for this
purpose, are amongst the most interesting and most ingenious to
which mechanical science has given birth. Working models, on an
enlarged scale, are almost necessary to make their action
understood by the unlearned reader; and, unfortunately, these are
not often to be met with. A very fine collection of such models
exists amongst the collection of instruments at the University of
Prague.
Instruments of this kind have been made to extend their
action over considerable periods of time, and to register not
merely the hour of the day, but the days of the week, of the
month, of the year, and also to indicate the occurrence of
several astronomical phenomena.
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