CONDITION OT THE MOON’S SURFACE.

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Mr. Mallet points out, lie discerns “ the true cause ofvolcanic heat. * As the solid crust sinks together tofollow down after the shrinking nucleus, the worhexpended in mutual crushing and dislocation of itsparts is transformed into heat, by which, at the placeswhere the crushing sufficiently takes place, the ma-

* “ In order to test the validity of his theory by contact withknown facts ” (says the Philosophical Magazine), “ Mr. Mallet givesin detail two important series of experiments completed by him ;—the one on the actual amount of heat capable of being developedby the crushing of sixteen different species of rocks, chosen so as tobe representative of the whole series of known rock-formations,from oolites down to the hardest crystalline rocks ; the other onthe coefficients of total contraction between fusion and solidification,at existing mean temperature of the atmosphere, of basic and acidslags analogous to melted rocks. The latter experiments wereconducted on a very large scale ; and the author points out thegreat errors of preceding experimenters, Bischoff and others, as tothese coefficients. By the aid of these experimental data, he isenabled to test the theory produced when compared with suchfacts as we possess as to the rate of present cooling of our globe,and the total annual amount of volcanic action taking place uponits surface and within its crust. He shows, by estimates whichallow an ample margin to the best data we possess as to the totalannual vulcanicity, of all sorts, of our globe at present, that lessthan one-fourth of the total heat at present annually lost by ourglobe is upon his theory sufficient to account for it; so that thesecular cooling, small as it is, now going on, is a sufficient prinrnmmobile, leaving the greater portion still to be dissipated by radia-tion. The author then brings his views into contact with knownfacts of vulcanology and seismology, showing their accordance. Healso shows that to the heat developed by partial tangential thrustswithin the solid crust are due those perturbations of hypogealincrement of temperature which Hopkins has shown cannot bereferred to a cooling nucleus and to differences of conductivityalone.”