THE 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[FOURTH SERIES.] 



JULY 1875. 



I. On the Temperature attainable by Rock-crushing and its Con- 

 sequences. By Robert Mallet, F.R.S.* 



IN developing the theory of volcanic heat and energy embraced 

 in his paper " On the Nature and Origin of Volcanic Heat and 

 Energy " (Phil. Trans. Part I., 1873), the main object of the 

 author was to prove that the annual work of secular contraction 

 in our globe, when transformed into heat, was more than ade- 

 quate for the supply of volcanic activity existing upon our planet. 

 While indicating generally the circumstances which must attend 

 as results of the descent of the exterior shell upon the more 

 rapidly contracting nucleus, it was not necessary to his argument 

 to follow into detail the mechanism of local dislocation and crush- 

 ing due to such descent. Nor would the limits of his paper admit 

 of his entering into much detail as to the circumstances attending 

 subterranean dislocation and crushing of rocky matter, or point- 

 ing out how some of these must greatly tend to exalt the tempera- 

 tures due to the transformation of the mechanical work locally 

 done. It was necessary to a truthful examination of the question 

 whether or not the annual supply of heat transformed from the 

 work of secular contraction were sufficient to meet the demands of 

 existing volcanic action, that he should not overrate the work so 

 transformed; and accordingly, in determining by experiment a 

 measure for the amount of that work, the author viewed the work 

 of crushing of unconfined or unsupported masses alone as the 

 source of heat, this method being that only which could afford 

 perfectly trustworthy experimental results. He paid no regard 

 to the additional work that must attend the collision and friction 



* Communicated by the Author. 

 Phil. Mag. S. 4. Vol. 50. No. 328. July 1875. B 



