quite likely to cool off more rapidly.

It is a very serious difficulty that at least one satellite does
not revolve in the right direction. How Neptune or Uranus could
throw their moons backward from its equator is not easily accounted
for. It is at least one Parthian arrow at the system, not necessarily
fatal, but certainly dangerous.

A greater difficulty is presented by the recently discovered satellites
of Mars. The inner one goes round the planet in one-third part of
the time of the latter's revolution. How Mars could impart three
times the speed to a body flying off its surface that it has itself,
has caused several defenders of the hypothesis to rush forward
with explanations, but none with anything more than mere imaginary
collisions with some comet. It is to be noticed that accounting for
three times the speed is not enough; for as Mars shrunk away from
the [Page 187] ring that formed that satellite, it ought itself to
attain more speed, as the sun revolves faster than its planets, and
the earth faster than its moon. In defending the hypothesis, Mitchel
said: "Suppose we had discovered that it required more time for
Saturn or Jupiter to rotate on their axes than for their nearest
moon to revolve round them in its orbit; this would have falsified
the theory." It is also asserted that the newly discovered planet
Vulcan makes an orbital in less time than the sun makes an axial
revolution.

In regard to one Martial moon, Professor Kirkwood, on whom Proctor
conferred the highest title that could be conferred, "the modern
Kepler," says: "Unless some explanation can be given, the short period
of the inner satellite will be doubtless regarded as a conclusive
argument against the nebular hypothesis." If gravitation be sufficient
to account for the various motions of the heavenly bodies, we have
a perplexing problem in the star known as 1830 Groombridge, now
in the Hunting Dogs of Bootes. It is thought to have a speed of
two hundred miles per second--a velocity that all the known matter
in the universe could not give to the star by all its combined
attraction. Neither could all that attraction stop the motion of
the star, or bend it into an orbit. Its motion must be accounted
for on some hypothesis other than the nebular.

The nebulae which we are able to observe are not altogether confirmatory
of the hypothesis under consideration. They have the most fantastic
shapes, as if they had no relation to rotating suns i