Let them turn aside for a moment from the nebulae in the sky to the conclusions to which philosophers had been irresistibly led by a consideration of the features of the solar system. We had before us in the sun and planets obviously not a haphazard aggregation of bodies, but a system resting upon a multitude of relations pointing to a common physical cause. From these considerations Kant and Laplace formulated the nebular hypothesis, resting it on gravitation alone, for at that time the science of the conservation of energy was practically unknown. These philosophers showed how, on the supposition that the space now occupied by the solar system was once filled by a vaporous mass, the formation of the sun and planets could be reasonably accounted for. By a totally different method of reasoning, modern science traced the solar system backward step by step to a similar state of things at the beginning. According to Helmholtz, the sun’s heat was maintained by the contraction of his mass, at the rate of about 220 feet a year. Whether at the present time the sun was getting hotter or colder we did not certainly know. We could reason back to the time when the sun was sufficiently expanded to fill the whole space occupied by the solar system, and was reduced to a great glowing nebula. Though man’s life, the life of the race perhaps, was too short to give us direct evidence of any distinct stages of so august a process, still the probability was great that the nebular hypothesis, especially in the more precise form given to it by Roche, did represent broadly, notwithstanding some difficulties, the succession of events through which the sun and planets had passed.
[Illustration: DR. WILLIAM HUGGINS, D.C.L., LL.D., PRESIDENT OF THE BRITISH ASSOCIATION.
Dr. Huggins is one of the most eminent astronomers of the present day, and his spectroscopic researches on the celestial bodies have had the most important results. He is a D.C.L. of Oxford, LL.D. of Cambridge, and Ph.D of Leyden. Dr. Huggins was born in 1824 and educated at the City of London School. He continued his studies, giving much of his time to experiments in natural philosophy and physical science. In 1855 Dr. Huggins erected a private observatory at his residence on Tulse Hill, where he has carried out valuable prismatic researches with the spectroscope.—Daily Graphic.]
The nebular hypothesis of Laplace required a rotating mass of fluid which at successive epochs became unstable from excess of motion, and left behind rings, or more probably, perhaps, lumps, of matter from the equatorial regions. To some thinkers was suggested a different view of things, according to which it was not necessary to suppose that one part of the system gravitationally supported another. The whole might consist of