MICHIGAN ACADEMY OF SCIENCE. 



97 



different types of monochromatic light at the same temperature or at 

 temperatures wliich are clianging sh)wly. 



UNIAXIALITY OF GYPSUM. 



Carefully oriented sections of colorless, transparent gypsum from the 

 following three localities — Ellsworth, Ohio; Eisleben, Germany; and 

 Cianciana, Sicil.v — were prepared and observations made for the tempera- 

 tures at which uniaxiality is to be noted for wave lengths ranging from 

 435 /A/x to 7()2jU./M. These observations are given in the following table: 



Table 1. 

 Temperature of Uniaxiality for Gypsum. 



Plate II shows the uniaxiality curve resulting from these observations. 

 While the observations for these sections are all of the same order, 

 nevertheless those for the Sicilian section seem to be a trifle higher than 

 4 



