Adams and Coker — Elastic Constants of Hocks. 117 



The averages of the determinations 

 made on each of the columns are as fol- 

 lows : 



E D a C 



a = 13,515,000 10,400,000 0-2838 5,270,000 



b = 14,170,000 10,945,000 '2840 5,525,000 



c = 14,170,000 11,085,000 "2870 5,505,000 



d — 13,197,750 10,076,000 -2812 5,155,000 



Av. 13,763,187 10,626,500 -2840 5,363,750 



The stress strain curves given by this 

 rock are shown in figure 11. As will be 

 seen from these curves, in its approach to 

 perfect elasticity the rock is comparable to 

 plate glass. 



The Elastic Constants of Glass. 



As in geophysical speculations, the earth 

 in respect to its rigidity and compressi- 

 bility is often compared to a globe of glass, 

 it seemed advisable to determine as accu- 

 rately as possible the elastic constants of 

 glass, for the purpose of comparing them 

 with the results obtained in the case of the 

 various rocks considered in this paper, 

 employing the same methods and carrying 

 out the work under exactly the same con- 

 ditions. This material lends itself excel- 

 lently to this method of measuring these 

 constants, provided the glass is free from 

 all irregularities in its substance and is 

 isotropic in character. The first difficulty 

 experienced was that of obtaining such a 

 glass. A,t the outset it was thought that 

 thick glass rods such as are used for vari- 

 ous purposes in the chemical and physical 

 laboratory might be employed, but al- 

 though several lots of the purest variety 

 of this material were procured, the glass 

 constituting it was found in all cases to 

 contain minute air bubbles, and when 

 examined between crossed nicols in polar- 

 ized light, showed brilliant colors — red, 

 yellow and blue. This indicated a state of 

 marked tension in the glass, evidently due 

 to the rod having been drawn when the 

 glass was in a viscous state, which was also 

 shown by the circular arrangement of the 

 little bubbles in the rod, following the 

 direction of its surface. Short lengths of 

 this rod moreover when tested in compres- 

 sion, so soon as the maximum load had 







© © © 







© © © 







© © © 





r^, 



-o © ^ O © 



: I S « S § 

















CM OS *C 







-" 







© © © 







o © © 







, © © © 





r-^> 



; ^ o Bo o © 

 oo 12 ** 9 £2 



co" ©~ 10" 



1—1 I— 1 



© © © 

 © © © 

 © © © 





^5 



' CO © oo © © 

 1 CO C° CM "* © 

 > • co • CO CM 



co" ©" xo" 



53 







53 





:* © © © 



™ © © © 



00 o © © 



53 





O 



^5 



X © © i-' o © 





_ CO O CM — ' -!>- 







C2 . . co ^_i 



'© 





© ^ ~ ~ 





O CO © io 



§ 





,_l l—l 



•K> 





© © © 



<$ 





© © © 





ncc c ,M°,° 





<o 



CO iC © oo © o 





OS i- CM CM © CO 





• • CO * © «o 







tJ«" — " ia 









.^2 







s> 





© © © 



4 





o © © 





n co ° - „°„ 



<o 



CO lO o © © © 



«•> 





©- X- CM CM J>- CO 



5» 





" * O * <— ' ^f 



i^ 











-tJh -— ' lO 



*s 





i— 1 i— 1 



"^ 







s 





© © © 



sq 





© © © 







CO CO °^J^ °^°^ 



<%r 



>■© 



00 to o"^ o o" 



GO 





OS ir- '>i CM cm CM 





' CO ' -C^ CO 



S 





-^" ©" icT 



3 





© © © 







© © © 



rO 



CO CO ©^ >— * ^ ©^ 

 CO lO o" 01 ©"©" 



•oi 





OS X- or, CM j^ cq 



o 





© 1— 1 -<*i 



© © © 



© © © 



r_| CO © — > © © 





53 



CO >o ^CO o"©" 



© ^ CO 9 1 © CO 



ir- rH CO 



co" ©" io 



© © © 



© lO © © 

 ^h CO © CO © © 





53 



co »o O ~co c ^ c r 

 <? *- io ™ ^ © 



CM CO^ — I 

 co" ©" lO 





d 



•£<^ b^^ 



