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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, 'Sve 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 



