K. MALLET ON HIS THEORY OF VOLCANIC ENERGY. 511 



38. Some Observations on the Eey. 0. Fisher's Remarks on Mr. 

 Mallet's Theory of Volcanic Energy. By* R. Mallet, Esq., 

 E.R.S., E.G.S. (Read June 23, 1875.) 



Mr. E. W. Hilgard, Professor of Geology in the University of 

 Michigan, in a paper " On some points in Mallet's Theory of Vul- 

 canicity" (Amer. Journ. Sci. vol. vii. June, 1874), has remarked 

 that that author's experiments ("On the Nature and Origin of 

 Volcanic Heat and Energy," Phil. Trans. 1873) "fail to carry 

 conviction as to the efficacy of this particular modus operandi in 

 reducing large masses of solid rock to fusion — unless essentially 

 supplemented by friction, and the heat produced within more or 

 less comminuted, detrital, or igneo-plastic masses by violent pres- 

 sure and deformation." 



The author's crushing- experiments had not for their object to 

 prove how high a temperature could be by this process and its 

 consequences attained in nature; and he has in his paper above 

 referred to entered into no details on this point of the subject; to 

 have done so would have too largely extended an already long paper. 

 Moreover he considered that every physicist interested in the 

 subject would follow out for himself the conditions and consequences 

 of the work of crushing in our globe's crust, and discern that there 

 was no physical impossibility in a temperature of rock-fusion resulting 

 therefrom. The object of the author's experiments was to fix what 

 was the annual minimum amount of heat available for vulcanicity 

 in our entire globe upon the mechanism which he has assigned. 

 Eor this purpose the crushing of cubes of rock in air was alone 

 available : his experiments prove what total minimum amount of 

 heat must be so produced, but do not, and never were intended to 

 prove what maximum amount of temperature may be locally at- 

 tained as a consequence of the circumstances following crushing as 

 it occurs in nature and deep beneath the surface ; and Professor 

 Hilgard remarks that the burden is thrown upon the opponents of 

 the author's theory to prove "the qualitative inefficiency of the 

 several modes of action that may come into play." 



The views expressed by Professor Hilgard anticipate those of the 

 .Rev. 0. Eisher brought before this Society, Professor Hilgard merely 

 pointing out that there is an absence of proof of experimental rock- 

 fnsion in the author's paper, whereas the Rev. 0. Eisher seems to 

 think that the author's theory is, in the absence of this proof alone, 

 to be wholly discredited. There are many things in Mr. Eisher's paper 

 read to this Society which have so little direct relevancy to the 

 author's views as to the nature and origin of volcanic heat, &c, that 

 he may pass them by here with but slight notice. It is wholly 

 immaterial to the author's views, for example, whether those of Sir 

 "W. Thomson and of General Barnard as to the rigidity of our globe 

 as a whole be true or false ; nor has it the slightest direct bearing 

 upon the author's views whether that which he has expressed as a 



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