consisted in
supposing that such inelastic bodies as meteoric stones might attain
the effective elasticity of a high order which was necessary to the
theory through the sudden volatilization of a part of their mass at an
encounter, by which what was virtually a violent explosive was
introduced between the two colliding stones. Professor Darwin was
careful to point out that it must necessarily be obscure as to how a
small mass of solid matter could take up a very large amount of energy
in a small fraction of a second.

HELMHOLTZ'S DISCOVERY.

The old view of the original matter of the nebulae, that it consisted
of a "fiery mist,"

"a tumultuous cloud,
Instinct with fire and niter,"

fell at once with the rise of the science of thermodynamics. In 1854,
Helmholtz showed that the supposition of an original fiery condition
of the nebulous stuff was unnecessary, since in the mutual gravitation
of widely separated matter we had a store of potential energy
sufficient to generate the high temperature of the sun and stars. We
could scarcely go wrong in attributing the light of the nebulae to the
conversion of the gravitational energy of shrinkage into molecular
motion. The inquisitiveness of the human mind did not allow us to
remain content with the interpretation of the present state of the
cosmical masses, but suggested the question--

What see'st thou else
In the dark backward and abysm of time?

What was the original state of things? How had it come about that by
the side of ageing worlds we had nebulae in a relatively younger stage?
Had any of them received their birth from dark suns, which had
collided into new life, and so belonged to a second or later
generation of the heavenly bodies?

LOOKING BACKWARD.

During the short historic period there was no record of such an event;
still it would seem to be only through the collision of dark suns, of
which the number must be increasing, that a temporary rejuvenescence
of the heavens was possible, and by such ebbings and flowings of
stellar life that the inevitable end to which evolution in its
apparently uncompensated progress was carrying us could, even for a
little, be delayed. We could not refuse to admit as possible such an
origin for nebulae. In considering, however, the formation of the
existing nebulae we must bear in mind that, in the part of the heavens
within our ken, the stars still in the early and middle s