‘ill 
colour by polarised light ; and upon his method of obtaining 
determinate flower-like forms, surrounded by a film of the 
uncrystalised salt. The novelty of the author’s system, con- 
sists in the following particulars : — he makes a nearly 
saturated solution, say of the double sulphate of copper and 
magnesia ; he dries rapidly a portion on a glass slide, allowing 
it to become so hot as to fuse the salt in its water of crystali- 
sation; there then remains an amorphous film on the hot 
glass. On allowing the slide to cool slowly, the particles of 
the salt will absorb moisture from the atmosphere, and begin 
to re-arrange themselves on the glass, commencing from 
points. “ If then placed under the microscope,” says the 
the Author, “ we shall see points starting up here and there, 
“ and from those centres, the crystals may be watched as they 
“ burst into blossom, and spread their petals on the plate.” 
Starting points may be made at pleasure by touching the 
film with a fine needle, to enable the moisture to get under 
it ; but this treatment renders the centres imperfect. If 
allowed to go on, the crystals would slowly cover the plate, 
or if breathed upon, they form immediately ; whereas, if it 
is desired to preserve the flower-like forms on a plain ground, 
as soon as they are large enough, development is suspended, 
by again applying gentle heat ; the crystals are then covered 
with balsam and thin glass, to be finished off as usual. The 
balsam must cover the edges of the film, or moisture will 
probably get under it, and crystallisation go creeping on. 
Many crystals which produce similar forms, cannot be 
preserved in balsam ; in the hyposulphite of soda they are 
very fine, and the Author is endeavouring to preserve them 
in castor oil. 
Mr. Sidebotham referred to the vegetable forms produced 
by Mr. Petschler, with bichromate of potash in gelatine, 
exhibited at the British Association Microscopical Soiree* 
Since then flower-like shapes had been obtained from nitrate 
of silver amongst the ramifications of the bichromate ; as it 
