322 Reneu'8 — Capt. C, E. Button — 



I^ IE V I IE ^VsT S . 



I. — Critical Observations on Theories of the Earth's Physical 

 Evolution. By Capt. 0. E. Dutton, U.S.A. (The Penn 

 Monthly. Philadelphia, May, 1876.) 



THE author remarks that there are few great problems in 

 physical science, which have been studied so long, and with 

 such meagre success, as that which involves the dynamical causes of 

 the present inequalities of the earth's surface. Of the effects of the 

 force which has produced these, we already possess considerable 

 knowledge. Of its origin we know but little ; unless the theory 

 which has recently attracted much attention, and of which Mr. 

 Mallet, F.E.S., is the most conspicuous advocate, be considered a 

 true solution. The earth is assumed to be a mass, which is hot 

 within and cold without, and to be continuously radiating into space 

 its interior heat. In consequence of this loss of heat from the interior, 

 the portions which suffer a loss of temperature contract ; while the 

 portions near the surface, remaining at a temperature due to their 

 position in space, suffer no change of volume. As the solid crust 

 sinks together to follow down the shrinking nucleus, the worh 

 expended in mutual crushing, and dislocation of its parts, is trans- 

 formed into heat, by which, at the places where the crushing 

 sufficiently takes place, the material of the rock so crushed, and of 

 that adjacent to it, is heated to fusion. The access of water to such 

 points determines volcanic eruption. Volcanic heat therefore is one 

 result of the secular cooling of a terraqueous globe, subject to 

 gravitation ; and needs no strange or gratuitous hypothesis as to its 

 origin. Mr. Mallet also brings within the range of the same system 

 of causation the origin of terrestrial features. They are unquestion- 

 ably associated ; and any theory must similarly connect them. 

 The questions which will be asked, and to which answers will be 

 offered, are : 



First, admitting that the earth is a cooling body, and that it is 

 contracting internally, is the cause appealed to quantitatively suffi- 

 cient to produce the effect ascribed to it ? 



Second, admitting (for the sake of argument only) that the 

 assio-ned cause is sufficient, does it explain, and is it consistent with 

 known facts, and the observed structure of the earth's surface ? 



In connexion with the first inquiry, it may be remarked that Mr. 

 Mallet has not attempted to indicate the stage, which the secular 

 coolino- of the earth has now reached, but has arbitrarily assumed it 

 to be an advanced one. This is quite necessary to the validity of his 

 hypothesis. For it is obvious that if the secular cooling has been 

 hitherto small, it is insufficient to explain the various known phe- 

 nomena of structure, which, if produced by contraction at all, would 

 have required a very great amount of it. 



Sir W. Thomson has made an application of a proposition in 

 Baron J. J. Fourier's " Theorie Analitique de la Chaleur " to the 

 case of a cooling globe. The particular problem which he proposed 

 was, What has been the duration of the cooling, and what is the 



