74 • Table 45. 



ELASTICITY OF CRYSTALS.* 



The formulae were deduced from experiments made on rectangular prismatic bars cut from the crystal. These bars 

 were subjected to cross bending and twisting and the corresponding Elastic Moduli deduced. The symbols 

 a /3 7) «i Pi 71 and a, /So fo represent tlie direction cosines of the length, the greater and the less transverse 

 dimensions of the prism wuh reference to the principal axis of the crystal. E is the modulus for extension or 

 compression, and T is the modulus for torsional rigidity. 1 he moduli are in grams per square centimeter. 



Barite. 



-^ = 16.130^+ i8.5i;3'+ 10.427* +2(38.79i3V' 4 15.217V +8.SSa"/3') 



loi" 



-Tp- = 69.520''+ 1 1 7.663' +116.467* + 2(20.16)3-7- + S5. 297V + ^-7-35"'''^') 



Beryl (Emerald). 



^" == 4.325 sin'^ + 4.619 cos*0+ 13.328 sm2^cos2^ [ ^^f ^ ^^^K^'^'^^ ^"?^u^ Y^'^''^' 

 L ^-^ ^ r \ ^ J rijj r rj the length, breadth, and thickness 



10**' , ., ^ oj .T 1 of the specimen make with the 



^j^= 15.00 -3.675 C0SV2- 17-536 cos-^cos^?>i [ principal axis of the crystal. 



Fluorspar. 



i^=l3.o5-6.26(a*+;3' + 7*) 



loi" 



= 5S.04 — 50.0S (/3 '7- + 7'-a- + «-)8-) 



T 



Pyrite. 



i^"-5.o8-2.24(a* + /3' + 7*) 



-^ — 18.60 — 17.95 (/3V + rofi + a^/32) 



Rock salt. 



^ = 33.48-9.66(a* + /3* + 7*) 



loW 



i^ = 1 54. 58 - 77-28 (3 7- + 7-a- +«-^-) 



Sylvine. 



ig-'3=75.i-48.2(a* + )3' + 7*) 



loio 



-^ = 306.0 — 192.8 ()3-7- + 7-a- + a-j3-) 



Topaz. 

 loW 

 -^ =4.34ia* + 3.46018* + 3.7717*+ 2 (3.8790V + 2.8567V + 2.39a^i3^) 



loi* 



-^ = 14.8S0* + 16.5^/3* + 16.457* + 30.89/3V + 40-S97-a2 + 43.5ia-j82 



Quartz. 



-^ = 12.734 (1—72)24. 16.693 (i — 7-)7^ + 9-7057* — 8-460/37 (3a2 — ;3-) 



loio 



— = 19.665 + 9.060702 + 22.98472712 — 16.920 [(7)81+ 371) (3001 — )83i) — 3272)] 



* These formulae are taken from Voigt's papers (Wied. Ann. vols. 31, 34, and 35). 

 Smithsonian Tables. 



