HELMHOLTZ'S DISCOVERY.
The old view of the original matter of the nebulæ, 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 nebulæ 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 nebulæ 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?