116 



SCIENCE-GOSSIP. 



[Max 1, 1SG5. 



MICROSCOPY. 



PnoFOSAL TO London MicROsconsTS. — It ap- 

 pears to me that some association amongst tlie 

 amateur microseopists of London is desirable, wliicli 

 shall afford greater facilities for the communication 

 of ideas and the resolution of difficulties than the 

 present Society affords, and which, whilst in no 

 respect hostile to the latter, shall give amateurs the 

 opportunity of assisting each other as members of 

 an amateur-society, with less i^retensions, holding 

 monthly meetings in some central locality, at an 

 annual charge sufficient to cover the incidental ex- 

 penses — say five shillings a year — on the plan of the 

 Society of Amateur Botanists. By the publication 

 of this letter the general feeling of the parties in- 

 terested will be ascertained, and by this future action 

 determined. — W. Gibson. 



N.B. — We insert our correspondent's commimi- 

 cation, and would be glad to hear from any micros- 

 eopists desirous of co-operating with him in carry- 

 ing out his proposition. — Ed. So. G. 



Mounting OrAQUE or Transparent Objects. 

 — In reference to a mode of mounting for opaque 

 objects I have found that, after trying card- 

 board, gutta percha-, india-rubber, ivory, moulded 

 shellac, &c., none answer my purpose so well, or 

 look so neat, as those which are to be made from 

 fishing-rod rings. My modtcs operandi is as follows : 

 With a common gun-wad punch, punch out the 

 paper, to form the back-ground, a little less than 

 the ring, but slightly larger than its internal 

 diameter. The paper need not be dead black, as, if 

 so, its texture will be so coarse as to show its rough- 

 ness with a 2-inch objective. A very dark bronzed 

 highly-finished paper will be found the best. Have 

 ready a number of the rings, blacked inside with 

 Brunswick black, those measuring i-inch external 

 diameter being most useful. Next, centre a slip 

 of glass on your turn-table, and with a little gum 

 fix the paper in the centre of the slide, and by the 

 time that you have thus papered, say six dozen, the 

 first slip will be ready for the next stage, when you 

 again centre on the turn-table, and just on the out- 

 side, but touching the paper, run a thin ring of gold- 

 size, upon which drop the prepared cell ; and so on 

 with the remainder. When all are done, place them 

 on wooden trays, and bake them on the top of the 

 oven. In the course of a day or two again gold-size 

 the cell, letting the size extend only a short distance 

 on the glass beyond the circumference of the cell. 

 When this second coat is dry, a third of Brunswick 

 black may be laid over the whole exterior, filling up, 

 as much as possible, the angle formed by the outer 

 wall of the ring and the surface of tlic glass. In 

 placing the object, a sufficiently small portion of 

 gum may be generally taken up with a fine brush, 

 just enough to make the object adhere firmly, and 



yet not to show beyond its margin. In fixing the 

 glass cover again use gold-size, as being probably the 

 most tenacious cement there is, and as being less 

 liable to " run in " than the majority of such. After 

 one or two applications, made at longish intervals, 

 the whole may be finished off with Brunswick black. 

 I say the applications are to be made at longish 

 intervals, because I find that most of my friends are 

 in far too great a hurry with their work, putting on 

 coat after coat long before the last application can 

 possibly be dry. Brunswick black and other brittle 

 cements should never be used where adhesion is of 

 the first consideration. As to the mounting of 

 transparent objects, I am now using the glycerine 

 jelly, recommended by Mr. Lawrence in the micro- 

 scopical Journal, and referred to in that, to the 

 working microscopist, indispensable little brochure, 

 "The Preparation and Mounting of Microscopic 

 Objects," by Mr. Davies, and in which work the 

 reader will find instructions for its employment. I 

 can certainly recommend it most highly as being 

 easily workable, clean, a most excellent preservative, 

 and the object quickly put up and finished; the 

 latter being a great desideratum with novices. If it 

 had no other advantage there is one greatly in its 

 favour, viz., that there is no fear of leakage. Whilst 

 confcrvoid growths — to which, it is said, the jelly is 

 somewhat liable, though I have not found it so 

 — might probably be entirely avoided by always 

 keeping the bottle closely corked, and carefully scaling 

 the object mounted by a rmg of cement. — /. E. IF. 



Granite. — Granite, generally and theoretically,' 

 consists of crystals of quartz, of felspar, and of mica 

 embedded in crystalline quartz. Practically, all 

 porphyritic rocks are called granites. In many of 

 these rocks the mica is repkrced by hornblende, the 

 result being the variety called Syenite. The njica 

 and hornblende are sometimes absent or present in 

 very small proportions. The quartz sometimes pre- 

 pondei'ates, and is sometimes almost absent. The 

 felspar is sometimes in distinct crystals and some- 

 times only crystalline. The felspathic portion of the 

 stone also is sometimes felspar proper, but occa- 

 sionally albite, in which the alkaline element is 

 chiefly soda instead of potash. The crystals vary in 

 size and in the mode of their distribution, so that 

 the granite may be coarse or fine grained. Some 

 kinds of granite are brittle, and others singularly 

 tough ; some very easily break along lines of natural 

 fracture, and are comparatively soft while yet fresh 

 from the quarry, while other kinds resist any regular 

 fracture, and are only reduced to a desired shape 

 with extreme difficulty, even when first obtained. 

 Chemically, true granite is a silicate of alumina and 

 potash, with a little iron and lime, and with soda 

 sometimes replacing tlie potash and magnesia the 



