If we observe a flat strand when the tide is ebbing, we shall
still find the waves moving towards the shore.
_Ornamental Fountain Clocks._
It is the same cause (that which produces the deceptive appearance of a
progressive motion in the waves of the sea) which makes a revolving
cork-screw, held in a fixed position, seem to be advancing in that
direction in which it would actually advance if the worm were passing
through a cork. That point which is nearest to the eye, and which
corresponds to the crest of the wave in the former example, continually
occupies a different point of the worm, and continually advances towards
its extremity.--This property has lately been prettily applied in
ornamental clocks. A piece of glass, twisted so that its surface acquires
a ridge in the form of a screw, is inserted in the mouth of some figure
designed to represent a fountain. One end of the glass is attached to the
axle of a wheel, which the clock-work keeps in a state of constant
rotation, and the other end is concealed in a vessel, designed to
represent a reservoir or basin. The continual rotation of the twisted
glass produces the appearance of a progressive motion, as already
explained, and a stream of water continually appears to flow from the
fountain into the basin.
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