476 0. FISHER ON MR. MALLEx's 



planes, or places, where movement and pressure together constituting 

 work are greatest." This is, no doubt, true. Suppose a column of 

 rock 100 miles long compressed, and that a length of 90 miles of the 

 rock is so much stronger than the remaining ten as to resist crushing. 

 Then all the heat produced would he developed in those ten ; but 

 not more could be developed than enough to raise each of them by 

 170°, and that would be the case with all the ten, so that no fusion 

 could arise. Indeed the form in which the objection to Mr. Mallet's 

 reasoning suggested itself to my mind on first reading his paper was 

 simply this. If crushing the rocks can induce fusion, then the cubes 

 experimented upon ought to have been fused in the crushing. And I 

 still adhere to that simple mode of expressing my objection. 



In arguing thus I have assumed, what appears to be assumed 

 by Mr. Mallet, that as soon as the rock is crushed the work is com- 

 pleted ; so that, as no more motion can be obtained, so no more heat 

 can be developed. The result of compressing a gas would be dif- 

 ferent. 



Prom § 135 to § 172 we have the description of a valuable series 

 of experiments upon the fusion and contraction on cooling of slags 

 and other substances*. It appears that the slags on leaving the 

 furnace were at about 4000° F., and at the period of incipient solidi- 

 fication at 3000° F., from which it seems that 2000° F., which is the 

 temperature assumed in § 133 for melting rock, is lower than the 

 experiments justify. 



From § 174 to § 181 comparisons are made between the heat lost 

 by the earth and the quantity of rock which would need to be crushed 

 to supply it. 



In § 175 it is calculated that the diameter of the earth has shrunk 

 by 189 miles, at least, in passing from a state of fusion at 4000° F. 

 to its present state. In this estimate I cannot concur, because it 

 assumes, as appears by making the calculation, for the ratio of the 

 original to the contracted volume, 1000 : 933, as given in § 161. 

 In other words, it assumes the entire globe to have cooled to the 

 temperature of 53° F., which is clearly inadmissible. 



From § 183 to § 201 we meet with a calculation to prove that 

 "the crushing of the earth's solid crust affords a supply of energy 

 sufficient to account for terrestrial vulcanicity," and " that the neces- 

 sary amount of crushing falls within the limits that may be admitted 

 as due to terrestrial contraction by secular refrigeration." 



But if I have succeeded in showing that crushing of the rocks 

 cannot fuse them, these propositions are beside the mark. 



There are, however, certain strictures which it appears nevertheless 

 desirable to make upon this part of the paper. In the first place no 

 allowance is made for energy expended in elevating any part of the 

 crust by corrugating it. The elevation taken account of is only that 

 of the formation of volcanic cones, and even in that elevation the 



* I have largely availed myself of Mr. Mallet's results in my late paper " On 

 the Inequalities of the Earth's Surface &c," already referred to, and take this 

 opportunity of expressing my obligation to him, not only for his important 

 published results, but for private information and valuable help. 



