332 Transactions. — Geology. 



belong to our solar world were, in the beginning of all things, 

 resolved into their elementary substance, and filled the whole 

 space of the system in which these spheres now move. Laplace, 

 who is said to have been ignorant of Kant's hypothesis, pub- 

 lished his " Exposition du Systeme du Monde " in 1796, in 

 which he referred the formation of our planetary system to a 

 gradual cooling and contraction of the atmosphere of the sun, 

 contending that this atmosphere previously extended, under the 

 influence of excessive heat, beyond the orbits of the farthest 

 planets. Mayer, in his " Celestial Dynamics," (published in 

 1848,) tells us that the Newtonian theory of gravitation, whilst 

 it enables us to determine, from its present form, the earth's state 

 of aggregation in the past, at the same time points to a source 

 of heat powerful enough to produce such a state of aggregation, 

 and teaches us to consider the molten state of a planet as the 

 result of the condensation of cosmical matter, and to derive the 

 radiant heat of the sun and the heat of the bowels of the earth 

 from the same sources. Those who are curious as to these 

 speculations will find a criticism of the various phases which 

 the Nebular Hypothesis, as a cosmogenetic theory, has assumed, 

 in Stallo's " Concepts and Theories of Modern Physics," 

 published as vol. xlii. of the International Scientific Series, in 

 which the objections to each of the views propounded in relation 

 to this hypothesis are pointed out and discussed. But the 

 general idea that our planetary system originated from the con- 

 densation of cosmical matter has been confirmed by, or at all 

 events receives strong support from, our recently acquired know- 

 ledge of the present condition of two of the largest of its 

 members, — namely, Jupiter and Saturn, and of that of our own 

 satellite. As to the latter, it is abundantly proved, that it is 

 composed of the cooled relics of a once intensely heated mass, 

 its whole surface giving evidence of extinct eruptive action. The 

 absence of any appreciable atmosphere around it leaves that 

 surface permanently unchanged, the ruggedness of the ejected 

 material in no degree effaced, or even moderated, by the distri- 

 bution of light volcanic ash, if any such substance happens to 

 exist upon it, of which I have considerable doubt. We also 

 now know that each of the two great outer planets, Jupiter and 

 Saturn, is still in a condition of intense heat, througbout its 

 whole mass. "We recognize," says Mr. Proctor, "in the 

 appearance of Jupiter the signs of as near an approach to the 

 condition of the earth, when as yet the greater part of her mass 

 was vaporous, as is consistent with the vast difference between 

 two orbs containing such unequal quantities of matter ;" and 

 the same author, speaking of the "great red spot" which has, 

 for some years past, excited the attention and curiosity of astro- 

 nomers, says : "It may well bo that the movements by which a 

 disturbed cloud-belt on Jupiter returns to its normal condition 



