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Mr. It. Mallet on Volcanic Energy. [June 20, 



cooling from higher temperature of the whole globe and from a thinner 

 crust gave rise in former epochs to mountain-elevation, in the present 

 state of things gives rise to volcanic heat. By the application of a theorem 

 of Lagrange, the author proves that the earth's solid crust, however great 

 may be its thickness, and even if of materials far more cohesive and rigid 

 than those of which we must suppose it to consist, must, if even to a very 

 small extent left unsupported by the shrinking away of the nucleus, crush 

 up in places by its own gravity and by the attraction of the nucleus. 



This is actually going on, and in this partial crushing, at places or depths 

 dependent on the material, and on conditions pointed out, the author 

 discovers the true cause of volcanic heat. As the solid crust sinks together 

 to follow down after the shrinking nucleus, the work expended in mutual 

 crushing and dislocation of its parts is transformed 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 are heated, even to fusion. The 

 access of water to such points determines volcanic eruption. Volcanic 

 heat, therefore, is one result of the secular cooling of a teraqueous globe 

 subject to gravitation, and needs no strange or gratuitous hypothesis as 

 to its origin. 



In order to test the validity of this view by contact with known facts, the 

 author gives in detail two important series of experiments completed by 

 him : — the one on the actual amount of heat capable of being developed 

 by the crushing of sixteen different species of rocks, chosen so as to be 

 representative of the whole series of known rock formations from Oolites 

 down to the hardest crystalline rocks ; the other, on the coefficients of 

 total contraction between fusion and solidification at existing mean tem- 

 perature of the atmosphere of basic and acid slags, analogous to melted 

 rocks. 



The latter experiments were conducted on a very large scale, and the 

 author points out the great errors of preceding experimenters, Bischoff and 

 others, as to these coefficients. 



By the aid of these experimental data, he is enabled to test the theory 

 produced when compared with such facts as we possess es to the rate of 

 . present cooling of our globe, and the total annual amount of volcanic action 

 taking place upon its surface and within its crust. 



He shows, by estimates which allow an ample margin to the best data 

 we possess as to the total annual vulcanicity of all sorts of our globe at 

 present, that less than one fourth of the total heat at present annually lost 

 by our globe is upon his theory sufficient to account for it ; so that the 

 secular cooling, small as it is, now going on is a sufficient primum motile, 

 leaving the greater portion still to be dissipated by radiation. The author 

 then brings his views into contact with various known facts of vulcanology 

 and seismology, showing their accordance. 



He also shows that to the heat developed by partial tangential thrusts 

 within the solid crust are due those perturbations of hypogeal increment of 



