74 TABLE 45. 



' ELASTICITY OF CRYSTALS.* 



The formulas 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 ft y, a t /3 t Vj and a 2 /3, y 2 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 crystal. E is the modulus for extension or 

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



Barite. 



18.51/8* + 10.427* + 2( 3 8.79l8V-F 15.217^ + 8.SS"/8-) 



1 17.66/8* +[i 16.467* + 2(20.i6/8V + 85.297^ + 1 



Beryl (Emerald). 



l = 4.3'S sin'* + 4.6.9 co* + I3 .3'8 rinV co* J 



io 10 of the specimen make with the 



=15.00-3.675 cosfc 17.536 cos2^cos 2 9i [ principal axis of the crystal. 



Fluorspar. 



i = 13.05- 6.26 (a* + 



T010 



^ = 58.04 - 50.08 (ft 

 Pyrite. 



= 18.60 - 17-95 (0V + 7- 2 + 

 Rock salt. 



- = 1 54.58 - 77-28 ( j8 V + 7 2 2 + 2 2 ) 



Sylvine. 



Ig- = 75-1 -48.2 (a* + ^ + 7 4 ) 



Tn io 



f^p = 306.0 192.8 (/8V + 7 2 2 + a 2 2 ) 



Topaz. 



^ = 4 . 34 ia 4 + 3. 4 6o)8 4 + 3-77 17 4 + 2 (3-879/8 V + 2.8567^ + 2. 39 a 2 ^) 



Tn io 



^r = I 4 .88a* + I6-54/3 1 + I6-457 4 + 3^90V + 40.897 2 2 + 43-5i< 2 2 



Quartz. 



ij = 1 2.734 (i - 7 2 ) 2 + 16.693 (i - 7^72 + 9.7057* - 8.460/87 ( 3 a 2 - 0-) 



io 10 



= 19.665 -f- 9.060732 + 22.9847V 16.920 [(7/8!+ 71) (3001 /8i) 



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

 SMITHSONIAN TABLES. 



