PROCEEDINGS OF SOCIETIES. 179 
temperature of about 60° Fahr., numerous foliated crystals radi- 
ating from centres will soon be seen to form, and, if the slide be 
examined minutely, other small round forms will be noticed, which 
have no connection with the foliated crystals, but which consti- 
tute the first stage of the spiral. (Fig. 1.) 
At 65° the foliated structures are lost, and the round erystals 
only are seen in great numbers, clearly showing a further advance 
in the direction of the spiral, and presenting a well-marked but 
curved black cross. (Fig. 2.) 
At 70° the spiral is still more marked. (Fig. 3.) 
At 80° to 90° the lines are smaller and more numerous, while 
the spiral is evidently more pronounced. (Fig. 4.) 
