The stampers and the projecting pieces on
the axis are removed, and a barrel of wood or metal, surrounding
part of the axis, and capable, at pleasure, of being connected
with, or disconnected from the axis itself, is substituted. The
rope which hitherto fastened the boat, is now fixed to this
barrel; and if the barrel is loose upon the axis, the
paddle-wheel makes the axis only revolve, and the boat remains in
its place: but the moment the axis is attached to its surrounding
barrel, this begins to turn, and winding up the rope, the boat is
gradually drawn up against the stream; and may be employed as a
kind of tug-boat for vessels which have occasion to ascend the
rapid. When the tug-boat reaches the summit the barrel is
released from the axis, and friction being applied to moderate
its velocity, the boat is allowed to descend.
54. Clocks occupy a very high place amongst instruments by
means of which human time is economized: and their multiplication
in conspicuous places in large towns is attended with many
advantages. Their position, nevertheless, in London, is often
very ill chosen; and the usual place, halfway up on a high
steeple, in the midst of narrow streets, in a crowded city, is
very unfavourable, unless the church happen to stand out from the
houses which form the street.
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