140 Mr. 0. Fisher's Remark* upon 



portionatcly under the enormous pressures to which a dis- 

 continuous mass at several miles depth may be subjected, we 

 can readily see that the transformed heat of friction produced 

 by internal movements taking place in such materials after 

 crushing has occurred, must be the source of a large amount of 

 heat over and above that originally due to the crushing itself." 

 It is evident from this passage that Mr. Mallet thought a 

 large value for friction was favourable to his theory (as 

 developed by Prof. Hilgard) ; and he afterwards generously 

 assumes the smaller value 0*5 for the coefficient. I purposely 

 gave him the advantage of the larger estimate. But I am 

 quite content that Mr. Mallet should make use of any co- 

 efficient of friction which he thinks admissible. 



The following passage strikes me as certainly unfair : — 

 u Somewhat further on we find the author overthrowing, 

 in the following sentence, the entire mathematical house of 

 cards which he has with so much parade erected. ' If, how- 

 ever, as is more likely, the crust rests upon a fluid or viscous 

 layer, the resistance to lateral motion will be much smaller ; 

 but we are not able to guess what it will be, so that we cannot 

 a priori assign a value to /*.' ' Why did not Mr. Mallet 

 quote the sentence which follows and qualifies this ? — " But a 

 probable estimate [for/x] maybe arrived at from the considera- 

 tion that a great circle of the sphere cuts on an average at least 

 three lines of weakness, as appears upon the inspection of a 

 ma}) showing the lines of volcanic action." In fact my 

 formula is general, and can be applied whether there be a 

 solid nucleus or a viscous substratum. 



It is well known that some physicists insist upon a solid 

 nucleus ; and no doubt Mr. Mallet would have been quick to 

 notice the omission had I not adverted to that case ; but by 

 altering the value of /z,, the formula equally well applies to the 

 case of a viscous layer beneath the crust ; and I have so 

 applied it, though Mr. Mallet has left it to be inferred that 

 this most important case has been overlooked by me. The 

 truth is that I have disproved the theory in this case as well 

 as in the other, taking the coefficient of friction as low as ^ ; 

 and seeing that Mr. Mallet suggests J, this value must surely 

 be small enough to satisfy him. 



Again, referring to my statement that, " if the work of descent 

 of the crust be not transformed into the heat of volcanic 

 energy, it may be asked, What becomes of it?" Mr. Mallet 

 objects to my reply, that part of it is transformed into heat 

 within the nucleus, — and argues that this cannot be, because 

 I assume that the nucleus itself is hotter than the heat of 

 vulcanicity. I suppose Mr. Mallet will admit that part of the 



