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 bending and twisting and the corresponding Elastic Moduli deduced. The symbols 

 a )3 y, a, j3, y, and o 0, V2 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 grammes per square centimetre. 



Harite. 

 io 10 

 -p- = 16.130* + 18.51/3' + 10.427* + 2(38.79/3V 2 -r 1 5-2i7-er + 8.88a-j8 2 ) 



lfj_ 6g.52a 4 + 1 17.66/8' +]i 16.467* + 2(20.i6/3-V + 85-297 ? a 2 + i27.35a-0 2 ) 



Beryl (Emerald). 



io 10 



-rr- =4.325 sin'0 -j- 4.619 cos 4 ^ -j- 13.328 sin 2 ^ cos 2 ? 



rr 



10 



io 



-rp- = I 5-00 3.67 5 COS*0 2 1 7- 536 COS 2 ? COS 2 9i 



Fluor spar. 



- = 13.05 6.26 (a* + j8 l + 7*) 



^- = 58.04 50.08 (/3V 2 + y-a- + a 2 )8 2 ) 



Pyrites. 



^- = 5.08 2.24 (a 4 + 0' + 7*) 



^ = 18.60 17.95 (fl'V + r' 2 + ' 2 )8 2 ) 



Rock salt. 



^ = 33.48 - 9.66 (a* + P + T 4 ) 



^r- = I 54.58 77.28 (0V 2 + 7' 2 - +' 2 2 ) 

 Sylvine. 



where <j> <t>i fa are the angles which 

 the length, breadth, and thickness 

 of the specimen make with the 

 principal axis of the crystal. 



-^- = 306.0 192. 



Topaz. 

 io 10 

 -^ 4.341 a 4 + 3 . 4 6oj8* + 3.7717*+ 2 (3.879/3 V+ 28. 5 6 7 V+ 2. 39 a^ 2 ) 



io 10 



- T = I 4 .88a + 16.54)8* + i6. 45 7 4 + 30.8 9 j8V 2 + 4P&9ry*a* + 43-5i 2 )8 2 



Quartz. 



io 10 



-g- = 12.734 (i 7 2 ) 2 + 16.693(1 7 2 ) 7 2 + 9.7057* 8.460/37 (3o 2 )8 2 ) 



io 10 



-- = 19.665 + 9-06072 2 + 22-9847'V 2 16.920 [(7/3 + 07i) (3i ^3i) 27-2)] 



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

 SMITHSONIAN TABLES. 



77 



