.MICHIGAN ACADEMY OF bCIEXCK. 



99 



Table 2. 

 Size of the Optic Angle of Glauberite for \'ari()iis Wave Lengths 



at Different Temperatures. 



T°C 



670mm 



Plate III shows full curves between 2.5° C and 98' C for 589, 656, 

 and 670/jifji and partial curves for 165, 486, and 527 /xfi. The full 

 curves correspond in general to those published earlier although the 

 observed uniaxialitv points are slio-htlv lower. This means that the 

 angles below uniaxialitv are slightly smaller and those above the 

 uniaxialitv point are slightly larger for any given temperature than those 

 previously recorded. The agreement between the new and the older 

 observations on glauberite is greater than in the case of gypsum, for both 

 series were made by using the same oil bath, namely one with^ a capacity 

 of about 150 c.c, and as uniaxialitj* takes place at lower temperatures, 

 constancy of temperature can be better maintained. 



UNIAXIALITV TEMPERATURES OF GLAUBERITE. 



Several series of observations were made of the temperatures at which 

 imi.'ixi.ility is to be observed for light ranging from 511/u./a to 687/ia/u.. 



