THEORY OF VOLCANIC ENERGY. 475 



been largely influenced by the cube experimented upon having been 

 free on four of its sides. If it had been confined in a box of its ex- 

 act size it might still have been crushed ; but the amount of descent 

 would have been in that case dependent solely upon the increase of 

 density which could be given to it after disintegration by the pressure. 

 If the box had beensomewhat larger, the plunger would have descended 

 further, and if the rock was altogether unsupported, as seems to have 

 been the case, further still. Now I do not question that the value of H 

 (the heat) found in accordance with the experiment is correct ; but I 

 do question, as already stated, the form of the experiment representing 

 at all closely what would happen deep in the earth's crust. It seems 

 to me the cubes should have been confined, and that the experiment 

 in § 99 more closely represents the case of nature. 



But I will accept the results as given in columns 26 and 28, which 

 give the final effects of crushing upon the temperature of the rock. 

 The mean number of British units of heat developed by crushing one 

 cubic foot of the harder rocks is there put down at 5650 ; and the 

 mean temperature by which a cubic foot of such rock would be raised 

 I make to be 172° F. Or if we take the particular kinds of rock 

 selected by Mr. Mallet (§ 133), these means are found by him to be 

 6472 and 184° F. And if the rock was previously at 300° F., taking 

 2000° as the fusing temperature, he makes 0-108, or rather above 

 one tenth, as the fraction of a cubic foot of rock which the heat 

 developed by crushing one cubic foot of rock could fuse. Or, to put 

 it otherwise, it would require the heat developed by crushing ten 

 volumes of rock to fuse about one. 



Here is the point at which I cease to follow the distinguished 

 author. He considers that the heat so developed may be localized, 

 and that the heat developed by crushing, say ten cubic miles of rock, 

 may fuse one mile. But, I ask, how so ? The work is equally dis- 

 tributed throughout. Why should not the heat be so also ? Or if 

 not, what determines the localization ? For example : suppose a 

 horizontal column ten miles in length and one in sectional area 

 to be crushed by pressures applied at its ends. Which of the ten 

 cubic miles is to be the one fused ? But if no cause can assign one 

 rather than another, it is clear that they will all be heated equally 

 by 170° F., and none of them fused. 



To take an analogous case by way of illustration : — Suppose a rail- 

 way train in motion with n wheels to be stopped by a single brake 

 in a given time. Heat enough may be developed to produce sufficient 

 rise of temperature in the brake to burn it. But if a brake be applied 

 to every wheel with an equal pressure on each so as to stop the train 



in the same time as before, each brake will be heated by -th of the 



n 



amount by which the one brake was heated in the first case ; and 



none of them need be burnt. And if some of them are not burnt, 



certainly the rest will not be so. If I may be allowed to use the 



word, the fallacy appears to lie in the application of the principle 



expressed in § 66, where we read : — " The work thus developed is 



transformed into heat ; that heat is greatest along those lines, or 



