uve, that there is a gradual extinction in
the light of the stars, amounting to a loss of 1/107 of the whole, in
the distance which separates Sirius from the sun. According to Struve,
this can be accounted for, "by admitting as very probable that space is
filled with an _ether_, capable of intercepting in some degree the
light." Is it not as probable that this extinction is due to planetary
dust, scattered through the pure ether, whose vibrations convey the
light,--the material atoms of future worlds,--the debris of dilapidated
comets? Does not the Scripture teach the same thing, in asserting that
the heavens are not clean?

The theory of vortices has had many staunch supporters amongst those
deeply versed in the science of the schools. The Bernoullis proposed
several ingenious hypothesis, to free the Cartesian system from the
objections urged against it, viz.: that the velocities of the planets,
in accordance with the three great laws of Kepler, cannot be made to
correspond with the motion of a fluid vortex; but they, and all others,
gave the vantage ground to the defenders of the Newtonian philosophy, by
seeking to refer the principle of gravitation to conditions dependent on
the density and vorticose motion of the ether. When we admit that the
ether is imponderable and yet material, and planetary matter subject to
the law of gravitation, the objections urged against the theory of
vortices become comparatively trivial, and we shall not stop to refute
them, but proceed with the investigation, and consider that the ether is
the original source of the planetary motions and arrangements.

On the supposition that the ether is uniformly dense, we have shown that
the periodic times will be directly as the distances from the axis. If
the density be inversely as the distances, the periodic times will be
equal. If the density be inversely as the square roots of the distances,
the times will be directly in the same ratio. The celebrated J.
Bernoulli assumed this last ratio; but seeking the source of motion in
the rotating central globe, he was led into a hypothesis at variance
with analogy. The ellipticity of the orbit, according to this view,
was caused by the planet oscillating about a mean position,--sinking
first into the dense ether,--then, on account of superior buoyancy,
rising into too light a medium. Even if no other objection could be
urged to this view, the difficulty of explaining why the ether should be
denser near