57. In mines, it is sometimes necessary to raise or lower
great weights by capstans requiring the force of more than one
hundred men. These work upon the surface; but the directions must
be communicated from below, perhaps from the depth of two hundred
fathoms. This communication, however, is accomplished with ease
and certainty by signals: the usual apparatus is a kind of
clapper placed on the surface close to the capstan, so that every
man may hear, and put in motion from below by a rope passing up
the shaft.
At Wheal Friendship mine in Cornwall, a different contrivance
is employed: there is in that mine an inclined plane, passing
underground about two-thirds of a mile in length. Signals are
communicated by a continuous rod of metal, which being struck
below, the blow is distinctly heard on the surface.
58. In all our larger manufactories numerous instances occur
of the application of the power of steam to overcome resistances
which it would require far greater expense to surmount by means
of animal labour. The twisting of the largest cables, the
rolling, hammering, and cutting large masses of iron, the
draining of our mines, all require enormous exertions of physical
force continued for considerable periods of time.
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