Adams and Coker — Elastic Constants of Rocks. 119 



constants. The figures obtained are set forth in the table on 

 p. 118. 



In this table a complete series of values obtained from each 

 specimen are given in double rows. When the average of all 

 these results is taken, the values obtained for the several con- 

 stants of plate glass are as follows : 



^=10,500,000; o- = 0-2273; B =6,448,000 ; (7=4,290,000 



The stress-strain curves given by one of the prisms is shown 

 in figure 12. In this figure I represents longitudinal compres- 

 sion and II lateral extension. 



Determinations of the cubic compressibility of glass, D, 

 have been made by other observers using various methods. 



9000 



• 7000 



q 5000 



3000 



10OO 











v^ 



^r 







































O 40 80 120 160 200 240 



STRAIN 



Fig. 11. Sudbury Diabase, stress strain curves. 



The results go to show that different varieties of glass vary 

 considerably in their compressibility. These determinations 

 may be tabulated as follows :* 



Everett 5,074,600 to 6,379,400 (C.G.S. = 3'5 to 4-4 X10 11 ) 



Araagat-coramon 



glass ______ 6,745,000 (-000002181 per atmosphere) 



Amagat-crystal 



glass 6,112,300 (-000002405 " " ) 



Tait 5,657,700 (-0000026 " " . ) 



As will be seen, the figures obtained for plate glass in the 

 present investigation lie a little above the average of the vari- 

 ous values here given, and are nearly those of the highest 

 value obtained by Everett. 



* See Everett, Illustrations of the C.G-.S. 'System of Units with tables of 

 Physical Constants. Macmillan & Co., 1902, pp. 60 to 64. The figures 

 there expressed in various units have been here recalculated into inch-pound 

 values. 



