1862.] 



85 



Slate rock 



Quartz rock 



( Hardest 

 I Softest . 

 f Hardest 

 I Softest . 



each rock of maximum and of minimum compactness and hardness, 

 so that the series of experiments upon the compressibility of these 

 rocks (from which the modulus is derived) assumes the following 



divarication, viz. : 



f B. Parallel to laminse, Table 2. 



1 A. Transverse to laminse, Table 1. 



J F. Parallel to laminse, Table 6. 



1 E. Transverse to laminae, Table 5. 



f D. Parallel to laminse, Table 4. 



I C. Transverse to laminae, Table 3. 



| H. Parallel to laminee, Table 8. 



1 G. Transverse to laminse, Table 7. 

 Involving thus eight distinct series of experiments. 



The compressions were conducted at the Royal Arsenal, Woolwich, 

 by the aid of the excellent American machine belonging to the Royal 

 Gun-factories, permission to use which was accorded to the author. 

 The specimens of rock submitted to pressure were all equal cubes 

 of 0*707 inch on the edge, presenting thus a surface on each side 

 of 0*5 square inch a dimension presenting facilities for tabular 

 reduction, &c. 



The cubes were cut from the chosen rock specimens (selected with 

 care as fairly representative) by means of the lapidary's wheel, and 

 had opposite faces rigidly parallel and equal. 



The pressures advanced by 1000 Ibs. per square inch of surface, 

 from zero up to the crushing point of the specimen ; and at each 

 advance the actual compression of the column of rock was measured 

 by instrumental arrangements that admitted of reading space to 

 0005 of an inch. The results are given in Tables numbered 1 to 8, 

 referred to above, and these are compared in two Tables numbered 

 9 and 10. 



The following are the mean compressions for each 1000 Ibs. per 

 square inch : 



