ME. EOBEET MALLET ON VOLCANIC ENEEGY. 
9.‘X 
C. Work of crashing, derived from experiments (Phil. Trans. 1862) on Holyhead Pocks. 
The hardest quartz rock (sp. gr. 2 - 656). 
Across lamination crushed with 37,000 lbs. on the square inch. 
Parallel with lamination . . 20,000 
2)57,000 
Mean of quartz both ways . 28,500 lbs. 
Then, on a cubic foot, 
144x28,500=4104000 lbs. to crush; 
and supposing the cube all crushed to powder and dissipated laterally, then this pressure 
would have descended 1 foot ; we therefore have the work of crushing the 1 foot cube 
= 4104000x1 = 4104000 lbs., 
and 
" 1 = 5 3 1 6 • 0 6 Fahr. in 1 lb. of water. 
This result, however, is below the truth, as the quartz rock was not crushed abso- 
lutely to powder. 
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2 H 
MDCCCLXilll. 
