Mr. E. Mallet on his Volcanic Theory, 21 



(Phil. Mag. July last), in reference to disintegrated ma- 

 terial, affords no warrant for the Rev. 0. Fisher's application 

 of it under conditions essentially different, while for his coeffi- 

 cient of adherence, or for the existence of adherence at all, he 

 offers no warrant whatever. The coefficient of friction, which 

 I have assumed in illustration only, is not 075, but 0*5 ; and 

 whether either of these be true or not, for the moderate pres- 

 sures of a few pounds per square foot as in Moriirs experiment, 

 they cannot be true, and in fact involve a physical impossibility, 

 where the pressure per unit of surface enormously exceeds the 

 crushing-resistance of the material as in his case, where the 

 pressure is that of a column 400 miles in height. Yet it is upon 

 these data that his argument rests, and by which he manages to 

 get rid of the largest portion of the work due to the descent of the 

 crust, and so to prove the residue insufficient for the production of 

 volcanic heat. There is nothing to warrant the supposition that a 

 crust 400 miles thick, which is the value our author assumes for 

 k y would be compressed equally throughout its depth or crush 

 simultaneously throughout its thickness ; nor can it be assumed 

 that volcanic activity is found uniformly diffused throughout the 

 depth of such a crust, but must be supposed, as I have shown 

 in my original paper (§ 87), to be confined principally to the 

 upper strata of the crust, where, as may easily be seen, in an 

 elastic and flexible crust local lateral displacements may take 

 place sufficient to produce crushing and volcanic action with- 

 out any dragging of the crust as a whole over the nucleus. 



If these data and others which I have not specified, as well 

 as several assumptions which the paper involves, be false, as 

 they undoubtedly are, then must the conclusions be false like- 

 wise, and this testing of my theory be but weighing it in a false 

 balance. 



But 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 //, " (page 316). Now, as the only 

 conceivable assumption that we can make is that adopted by 

 all physical geologists, namely that a solid crust passes by an 

 intervening viscous layer into a hotter nucleus below it, so 

 this statement on the part of the Rev. O. Fisher is to admit 

 that his whole mathematical argument is baseless and worth- 

 less. It seems to me a notable example of the misuse of ma- 

 thematics which Professor Huxley, in one of his addresses as 

 President of the Geological Society, not less wittily than truly 



