78 TABLE 54. 



ELASTICITY OF CRYSTALS. 



Some particular values of the Elastic Moduli are here given. Under E are given moduli for extension or compression 

 in the directions indicated by the subscripts and explained in the notes, and under T the moduli for torsional 

 rigidities round the axes similarly indicated. 



(a) REGULAR SYSTEM.* 



(6) RHOMBIC SYSTEM.|| 



In the MONOCLINIC SYSTEM, Coromilas (Zeit. fur Kryst. vol. i ) gives 



G sum 1 Emax ~ ^ 7 X io 6 at 21.9 to the principal axis. 

 I ^ = 313X106 at 75-4 



EmM == 22I 3 X lo6 m the P rmc iP al ax ^ s - 



Emm = 1554 X io 6 at 45 to the principal axis. 



Mica 



In the HEXAGONAL SYSTEM, Voigt gives measurements on a beryl crystal (emerald). 

 The subscripts indicate inclination in degrees of the axis of stress to the principal axis of 

 the crystal. 



E = 2165X108, 45=1796X106, E 90 = 2312X106, 

 TO = 667 X io 6 , Tgo = 883 X io 6 . The smallest cross dimension of the 

 prism experimented on (see Table 82), was in the principal axis for this last case. 



In the RHOMBOHEDRIC SYSTEM, Voigt has measured quartz. The subscripts have the 

 same meaning as in the hexagonal system. 



Eo = 1030 X io 6 , E_ 45 = 1 305 X io 6 , E+ 45 = 850 X io 6 , Ego = 75 X io 6 , 



To = 508 X io 6 , T 90 = 348 X io 6 . 

 Baumgarten 1" gives for calcspar 



Eo = 501 X io 6 , E_ 45 = 441 X io 6 , E + 45 = 77 2 X io 6 , E 9 o = 79 X io 6 . 



* In this system the subscript a indicates that compression or extension takes place along the crystalline axis, and 

 distortion round the axis. The subscripts b and c correspond to directions equally inclined to two and normal to the 

 third and equally inclined to all three axes respectively. 



t Voigt, "Wied. Ann." vol. 31, 34-35; 36, 642. 



i Koch, ''Wied. Ann." vol. 18. 



Beckenkamp, " Zeit. fur Kryst." vol. io. 



|| The subscripts i, 2, 3 indicate that the three principal axes are the axes of stress ; 4, 5, 6 that the axes of stress 

 are in the three principal planes at angles of 45 to the corresponding axes. 



f Baumgarten, " Pogg. Ann." vol. 152. 



SMITHSONIAN TABLES. 



