138 Mr. 0. Fisher's Remarks upon 



Specific Gravity of some of the Trap Rocks, — In the paper 

 by Professor Dana before cited, the specific gravity of one 

 variety of trap from this province, taken by myself for his 

 purpose of comparison, is given. I may conclude with some 

 additional examples, taken at about 60° Fahr. 



Spec. grav. 



1. Columnar trap, one weathered surface. West \q. 994 



side of Digby Gut J 



2. Crystalline trap, massive, above amygdaloid. \9.9p 9 



Gulliver's Hole, Digby Neck .... J 



3. Crystalline trap, massive, above amygdaloid, 1 £.91 g 



not very broken. Point Prim, Digby Gut J 



4. Crystalline trap, massive, above amygdaloid, 1 



newly broken. East of Sandy Cove, Digby > 2*915 

 Neck ) 



5. Amygdaloid. Hall's Harbour 2*747 



6. „ Peter's Point, Margaretville . 2*697 



7. „ Partridge Island 2*659 



XVII. Remarks upon Mr. Mallet's Strictures on the Mathema- 

 tical Test applied to his Theory of Volcanic Energy by Mr. 

 0. Fisher. By Mr. 0. Fisher, Clh, F.G.S* 



MR. MALLET'S theory of volcanic energy is essentially 

 a question of " how much ? " which can only be decided 

 by mathematical calculation. He has himself applied the me- 

 thod to the problem in his great paper ; so that any argument 

 against that mode of treatment of the subject lies against him- 

 self as well as against me. His general remark respecting 

 the applicability of mathematical reasoning seems intended to 

 reassure that class whom he describes towards the end of his 

 paper as persons upon whom mathematical symbols exercise 

 a sort of fascination like that of the serpent's glance upon 

 small birds. He would bid them shake off their fear and be 

 free ; for he tells them " mathematical reasoning is an admir- 

 able and potent instrument for the discovery of truth, when 

 the data upon which it is founded are exact, sufficient, anc 

 such as are sure to exist in nature. But all its validity de- 

 pends upon these data," which we all know are usually un- 

 attainable. As a contrast to this description, I give Thomsor 

 and Tait's account of the matter. 



" Until we know thoroughly the nature of matter, and th( 

 forces which produce its motions, it will be utterly impossible 

 to submit to mathematical reasoning the exact conditions 



* Communicated by the Author. 



