178 PROCEEDINGS OF SOCIETIES. 
temperatures. I have ventured to apply the term “ spiral erystal- 
lization” to this peculiar and very beautiful series of phenomena. 
The first and most difficult stage of the process consists in eva- 
porating a solution of sulphate of copper in such a way that the 
evaporation be not conducted too slowly, and that the heat em- 
ployed be not excessive. By steering warily between these two 
extremes, we avoid on the one hand crystallization of the solution, 
on the other the formation of small granular masses, which cover 
the slide and spoil it for future operations ; and we are enabled to 
Fig. 2. 
obtain an uncrystallized film, out of which the different crystal- 
line forms under consideration may presently develop themselves. 
If, now, such a film be subjected (after the manner indicated in 
my paper contained in the April number of this Journal) to a 
