The planets, then, have no appreciable, relative velocity in space, and
for this reason do not produce mechanical waves; and, if they become
capable of doing so through a peculiar energy developed at their
surface, as in the case of the sun, they are still too weak to give very
perceptible effects. The satellites, likewise, have relatively too
feeble velocities.
The comet, on the contrary, directly penetrates the solar waves, and
sometimes has a relatively great velocity in space. If its proper
velocity be of directly opposite direction to that of the ethereal
mass's rotation, it will then be capable of producing sufficiently
intense mechanical effects to affect our vision.
VIII.--Finally, seeing the slight distances at which these stars pass
the sun, the attraction upon the comet and its satellites may be very
different, and the velocity of rotation of the latter, being added to or
deducted from that of the forward motion, there may occur (as in the
case shown in Fig. 6) a separation of a satellite from the principal
star. The comet then appears to separate into two, and each part follows
different routes in space; or, as in Fig. 7, one of the satellites may
either fall into the sun or pursue an elliptical orbit and become
periodical, while the principal star may preserve a parabolic orbit, and
make but one appearance.
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