[Illustration: VI]
The spiral under consideration may be represented practically. If to a
vertical pipe we adapt a horizontal one that revolves with a certain
velocity, and throws out water horizontally, it will be understood that,
from a bird's eye view, the jet will form a spiral. Each drop of water
will recede radially in space, the spiral will keep forming at the jet,
and if, through any reason, the latter alone be visible, we shall see a
nearly rectilinear jet that will seem to revolve with the pipe.
Finally, if the jet be made to describe a curve, m n (Fig. 4), while it
is kept directed toward the opposite of a point, c, the projected water
will mark the spiral indicated, and this will continue to widen, and
each drop will recede in the direction shown by the arrows.
[Illustration: VII]
VII.--It seems to result from this explanation that all the planets and
their satellites ought to produce identical effects, and have the
appearance of comets. In order to change the conditions, it suffices to
admit that the ethereal mass revolves in space around the sun with a
velocity which is in each place that of the planets there; and this is
very reasonable if, admitting the nebular hypothesis, we draw the
deduction that the cause that has communicated the velocity to the
successive rings has communicated it to the ethereal mass.
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