128 PROCEEDINGS OF SOCIETIES. 



the development of tlie embryo, as sometimes occurs amongst higher 

 animals. 



The Secretary read a Paper, by Mr. Thomas Davies of Warrington 



on Crystallization. 



Mr. Davies treats more particularly upon some of the double salts, 

 which show beautiful combinations of form and colour by polarized 

 light ; and upon his method of obtaining determinate flower-like, 

 forms, surrounded by a film of the uncrystallizcd salt. The novelty 

 of the author's system, consists 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 

 crystallization ; 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 author, " we shall see points 

 starting up here and there, and from those centres the cr3'stals 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 ofi" as usual. The balsam must cover the edges of the film, 

 or moisture will probably get under it, and ci'ystallization go creep- 

 ing on. 



Many crystals which produce similar forms cannot be preserved 

 in balsam ; in the hyposulphite of soda they are vei-y fine, and the 

 author is endeavouring to preserve them in castor oil. 



IMr. 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 ramifi- 

 cations of the bichromate ; as it is an interesting subject, he should 

 endeavour to bring it before the next meeting. 



The discussion "On the cause of metallic lustre upon the wings 

 of the Lepidoptera" was resumed. Mr. Latham stated that he saw 

 no reason to alter the views he had expressed ; but since the last 

 meeting Mr. Watson bad called his attention to an article in the 

 'Annales des Sciences Naturelles' for February, 1835, by Bernard 

 Dechamps, " Sur les Ailes des Lepidopteres," which contains much 

 information upon the scales and the cause of their brilliance; he 

 (Mr. Latham) had translated and printed extracts from the paper ; 

 copies were handed round to the members present, and may be had 

 (gratis) at the Society's rooms, or from the Secretary of the Micro- 

 scopical Section. 



