LITERARY NOTICES. 



563 



intervene before the separation of another 

 annular mass." ' None of these rings could 

 long remain of uniform thickness. Each 

 would attenuate in some part, and finally 

 rupture, resolving itself into a mass that 

 would possess a rotary motion, the direction 

 of which would be determined by the rela- 

 tion of the velocities of the outer and inner 

 zones of the ring. 



Part II, " Planetology," occupies about 

 half the volume. In the first chapter of it, 

 certain observed phenomena of the solar sys- 

 tem are enumerated which accord with the 

 requirements of the nebular theory, and ob- 

 jections to the theory are answered. For 

 the retrograde motions of the satellites of 

 Uranus and Neptune our author advances 

 several explanations : 1. It is entirely con- 

 ceivable that both the Uranian and Neptu- 

 nian systems should have suffered a tilting 

 through more than a right angle by the in- 

 fluence of some powerfully attracting body 

 passing in the neighborhood. 2. The coa- 

 lescence of two or more spheroids may have 

 tilted the axis of the resultant planet, and 

 its whole system of satellites would be cor- 

 respondingly tilted. 3. Certain relations 

 of density, distance from the center of the 

 nebulous mass, breadth of ring, and ve- 

 locity might cause retrograde motion in the 

 earlier stages of the evolution of a nebula 

 of a certain magnitude. The next chapter 

 describes the passage of a gaseous planet 

 to the molten phase, the solidification of its 

 core from pressure of the superincumbent 

 portions, the incrustation of its surface, and 

 the transformations of this crust. A large 

 influence on planetary history is ascribed to 

 tidal action, a tide being defined as "the 

 prolateness of a body resulting from the 

 attraction of another body." Coming to 

 some special considerations of the planetary 

 bodies in the solar system, Professor Win- 

 chell mentions three independent conceiva- 

 ble causes for the molten condition in which 

 a part of the earth's substance evidently is : 

 ' There may be a zone too deep for solidifi- 

 cation by cooling, and too shallow for solidi- 

 fication by pressure. ... In the next place, 

 we may suppose that at all depths beneath 

 the surface the pressure is such that the 

 fusing-point is higher than the actual tem- 

 perature, so that a state of solidity exists. 

 . , . We may conceive that heat and fu- 



sion result from some mechanical crushing 

 pressure." In regard to this last theory he 

 says, further : " But a cause of crushing press- 

 ure which seems to me more adequate than 

 secular cooling is suggested by Sir William 

 Thomson's and Archdeacon Pratt's, and, 

 we may add, Professor G. H. Darwin's, dem- 

 onstrations of tidal effects in a globe as 

 rigid as steel or glass. May not the tidal 

 deformations of the earth's crust be the 

 source of the internal heat which manifests 

 itself in fluidity ? The whole value of the 

 lunar tidal oscillation in a yielding globe 

 should be about fifty-eight inches. In a 

 globe as rigid as glass it should, therefore, 

 be about 34"8 inches, and, in one as rigid as 

 steel, 1933 inches. The whole tidal oscil- 

 lation under the joint maximum influence 

 of the sun and moon in a perfectly yielding 

 globe would be about 8T2 inches. The 

 amount in a globe of glass would, therefore, 

 be, when at a maximum, 48'72 inches, and, 

 in a globe of steel, 27"06 inches. Should 

 the terrestrial globe yield to the extent of 

 any one of these amounts, the crushing 

 effect experienced by the superior zones 

 of the crust would not be uniformly distrib- 

 uted, since variations in structure and hard- 

 ness and surface configuration would pre- 

 serve certain portions from any change, and 

 the whole amount of the interstitial dis- 

 placements would be accumulated in the re- 

 maining portions. It does not seem at all 

 improbable that the transformation of such 

 enormous mechanical force into heat should 

 suffice to bring to a state of fusion volumes 

 considerable enough to answer all the re- 

 quirements of the thermal manifestations 

 of modern times, as well as the terrestrial 

 movements of modern earthquakes." From 

 an examination of the planetology of the 

 moon he concludes that " lunar history must 

 have presented characteristics widely di- 

 vergent from those of terrestrial history ; 

 and in this divergence the tenuity of the 

 moon's atmosphere has performed a part 

 quite comparable with the energetic work of 

 the tides. . . . 



" The question of the habitability of other 

 worlds has generally been discussed from 

 the assumption that all other corporeal be- 

 ings must be clothed in flesh and bones 

 similar to those of terrestrial animals, and 

 must be adapted to a similar physical envi- 



