Correspondence — Mr. Alfred SarJcer. 431 



me that the illustration is not apt. The amount of work to which 

 I refer must be expended on bending and breaking the particular 

 mass of rock under consideration, and in shearing the parts of it 

 past one another, and not on the rock outside of it. Hence the 

 energy which is its equivalent has been introduced into the mass ; 

 and, energy being indestructible, none of it is lost, and there is 

 now more energy in the mass than there was before. The question 

 which I proposed was simply, what form does that energy take ? 

 Is it heat ? or is it, as I (perhaps rashly) enquired, chemical energy ? 



Dr. Irving says that both Mr. Harker and myself have overlooked 

 the one great factor of metamorphism, viz. superheated water. I do 

 not think we either of us proposed to discuss all the causes of meta- 

 morphism, but only the mechanical. 0. Fisher. 



Harlton, Cambridge, 11 July, 1891. 



DYNAMO-METAMORPHISM AGAIN. 



Sir, — A short space will suffice for what I have to say in reply 

 to Dr. Irving (p. 296). I am sorry to have misunderstood, or, as 

 he phrases it ' misrepresented,' him as assuming that the whole of 

 the work passes into heat. I am not sure that even now his position 

 is clear to me. His dictum " chemical combination must generate 

 heat " is intelligible, though, as Mr. Fisher has pointed out, by no 

 means universally accepted by chemists ; but simple combination 

 does not cover any of the chemical changes that characterize the 

 metamorphism of rocks. These are "much more complex," and if 

 Dv, Irving believes that in these cases there is always, on the 

 balance, a positive amount of heat generated, he believes that for 

 which no proof whatever is offered. 



It is possible that some of the differences between Dr. Irving and 

 myself would resolve into a question of words, if his language were 

 more intelligible to me ; but unfortunately his usage of physical 

 terms often bears no relation to the definitions in use among physicists. 

 " Intensity of heat " seems to mean temperature, but what are we 

 to make of the expression (used in taxing another correspondent with 

 confusion of thought) "the energy is presented in the mechanical 

 form of pressure " ? The simple word * deformation ' also appears 

 to be employed in some occult sense. 



The experiments of Cailletet and Pfaff which I cited are the 

 same as those referred to in the " Report on Slaty Cleavage " mentioned 

 by Dr. Irving. They seem to establish that increased pressure 

 retards chemical changes involving a diminution of density, while 

 Spring's researches tend to show that pressure assists changes in- 

 volving an increase of density. The two conclusions appear to me 

 not contradictory, but complementary parts of one law. As regards 

 Spring's experiments, Dr. Irving has ludicrously misunderstood me 

 when he implies that I deny the generation of heat by friction 

 during the compression. What I said was that the heat so generated 

 was carefully removed (by conduction). As Major-General McMahon 

 points out (at p. 90 of this volume), M. Spring himself seems to 

 have changed his views as regards the significance of his work, but 



