Table 82. 

 ELASTICITY OF CRYSTALS.* 



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

 were subjected to cross bendinj; and twislini; and the corresponding Elastic Moduli deduced. The symbols 

 a ^ y, 0| (3, y, and a., /S, y._, represent the direction cosines of the length, the greater and the less transverse 

 dimensions of^ the prism with reference to the principal axis of the cr>'stnl. E is the modulus for extension or 

 compression, and T is the modulus for terminal rigidity. The moduli are in grammes per square centimetre. 



Barite. 



-j^ = l6.i3a<+ 18.51^'+ 10.427^ + 2(38.79)3-72+ 15-217-02 +8.S8a2/32) 

 ^ = 69.520*+ ii7.66)3'+;ii6.467< + 2(20.i6/3V + 85.297V+ 127. 35o2)8-') 



Berj'l (Emerald). 



loio 



jT- =4.325 sin*^ + 4.619 cos''^ + 13-328 sin20 cos^^ 

 310 



TT- = 15.00 3.675 C0S*^2 — 17-536 COS'-0 COS^^i 



where ^ ^1 (p2 are the angles which 

 the length, breadth, and thickness 

 of the specimen make with the 

 principal axis of the crystal. 



Fluor spar. 



i^" = 13.05 -6.26 (a* +i8< + y») 



10 



10 



^ = 58.04 - 50.08 ()3V- + 7-a- + a2/3-') 



Pyrites. 



i|L' =5.08- 2.24 («^ + 18' + 7^) 



'-^ = 18.60 - 17.95 (/3-V + ra- 4- a2/32) 



Rock salt. 



'-^ = 33.48 - 9.66 («4 + /3* + 7*) 



'-^ = 1 54.58 - 77-28 (^-V + 7-«" +a-/8-) 



Sylvine. 



i^' = 75-i-48.2(a4+/3i + 7*) 

 low 



-7j^ = 306.0 — 192.8 (/3V + yV + a2j32) 



Topaz. 



loio 



-^ = 4-341 a^ + 3-460/3* + 3-7717*+ 2 (3-87918-7-+ 28.567V + 2.39a2i32) 



10^ 



-Y = l4-8Sa< + 16.54/3' + 16.457* + 30.S9/3272 + 40.897202 + 43.5102/32 



Quartz. 



^'=12.734 (I -7-)2+ 16.693 (I — 7')7- + 9-7057* — 8-460/87 (3o2-|32) 

 loi" 



"Y" = 19-665 +- 9.060702 + 22.98472712 — 16.920 [(7/8 + /371) (3001 — $pi) — poji)] 



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

 Smithsonian Tables. 



77 



