PROCEEDINGS OF SOCIETIES. 137 
soria; crystals; photographs; and a variety of other objects of 
a miscellaneous character. 
The evening was far advanced before the various objects were 
exhausted ; and, on retiring, the visitors expressed so much satis- 
faction with the exhibition that it is probable a similar meeting 
will be held at the close of the session, at which period of the 
year (summer) many natural objects which cannot now be pro- 
cured will be obtainable. 
J.W. Acnew, M.D., Hon. See. 
Oxrorp Mtcroscopicat Sociery. 
On the CRYSTALLIZATION, af VARIOUS TemMPppRATURES, of the 
Dovste Sant, SutpHate oF Maewnesia aad SULPHATE OF 
Zinc. By Mr. THomas. 
ArtER making experiments according to Mr. Davies’s method, 
as explained in the ‘ Microscopical Journal’ for July last, I left 
one of the slides, with which I had been working, on my table for 
about half an hour. The sun was shining on the table at the 
time. On looking at the slide I found that crystallization had 
taken place; and, on examination under the microscope with a 
2-inch object-glass, I discovered what seemed to be a remarkable 
change in the form of the black cross, viz., that instead of running 
straight across the axis, as is generally the case in crystals with 
one axis, the two arms appeared to approach the centre, and then 
suddenly curve back, much in the same way as in a crystal of 
nitre. Also I noticed that, in other crystals on the same slide, 
each arm of the cross on approaching the centre made a slight 
curve, then passed through and formed a similar curve on the 
other side. It was from seeing accidentally this arrangement 
that I was induced to make a series of experiments at various 
temperatures with a Bunsen’s gas-burner and a stand on which 
I could arrange the slides at various distances, a thermometer 
being placed as close as possible to the slide under observation. 
At about 75° Fahr. I find that the arms of the cross are curved 
in the singular form here represented (see diagram 1). It seems 
also that the two salts combine at this temperature in two pro- 
portions, to form two distinct crystals, one having a distinct axis 
with a considerable amount of double refraction, which may be 
called crystal a (see diagram a) ; the other being in the form of 
rounded masses with small foliations and a less amount of double 
refraction, which may be called crystal B (see B). The latter, 
whose details come out more slowly, and, as a rule, from the 
circumference to the centre, constitutes a limit or boundary, as 
it were, to the former, which radiates invariably from the centre 
to the circumference. This, it seems, shows clearly that the two 
