^Zmll.TanTisw!''] NOTES AND MEMORANDA. 51 



was recently exhibited to tlie Society by Mr. Slack, consists of two 

 brass plates, S^^in. long by l2iii' wide, between which is j^laced a 

 brass disk with an aperture in the centre, in which is placed a thin 

 film of Mica. By placing the Selenite imdcr this stage and the object 

 upon it, and revolving the milled edge of the rotating disc, a very 

 great variety of colour will be obtained. The Mica appears to have 

 the power of developing or drawing out the colour in the Selenite. 

 It will be observed that by using this piece of apparatus the 

 polarizer is not touched, but by altering the angles of the polarizing 

 prisms the variety of tints and coloiu's will be still further increased. 

 The stage can be used with an ordinary selenite or with any sliding 

 and compound selenite stages. It is made by Mr. Swift, of Kings- 

 land Road, London. 



Vegetable Hairs. — These structures offer our readers an excellent 

 field for easy and interesting work, and as an introduction to the 

 subject we commend to their notice an illustrative and good paper, 

 " Vegetable Hairs," in ' Science Gossip ' for December. 



Brass Cells. — Mr. T. W. Wonfor, the well-known secretary of 

 the Brighton and Sussex Natural History Society, considers that 

 cells made of india-rubber bands and such-like materials are use- 

 less if required to last. He recommends brass cells.* These, he 

 says, which are cheap and easy to fix, he makes from brass rings ; 

 he used to employ different sized curtain-rings, until he became 

 acquainted with those referred to. They are used by tailors as button 

 moulds, and can be purchased in three sizes, at a woollen-draper's or 

 tailor's trimming warehouse, at from 10<^. to Is. 4fZ. per gross ; and 

 therefore as regards cheapness can compete with the endless bands. 

 As to the mode of fixing : this is done by marine glue, or one of the 

 many cements used for fixing glass and brass, or repairing glass or 

 china. He prefers the marine glue, because when properly manipu- 

 lated it never fails, and the slide will sooner break than the cell 

 come off. His modus operandi is as follows : first, centre a batch of 

 slides, and cut some marine glue into pieces the size of a pin's head ; 

 then, with wooden forceps, seize one end of the slide, drop a ring 

 on centrally, place three or four pieces of glue at intervals outside, 

 and tou^ch the brass ring ; hold the slide over a spirit-lamp, until the 

 glue by capillary attraction runs imder (care must be taken not to 

 bake too much) ; then drop the slide on wood to cool, when tlie super- 

 fluous glue may be removed with a knife. To fix the glass cover, 

 paint the ring with gold-size, and when tacky, drop on the cover ; 

 when diy, give it a coat of gold-size, and finish it off with asphalte or 

 coachmaker's varnish. If required for fluid, he either paints the 

 inside with gold-size or with electroplate before fixing. If a deeper 

 cell is required, he cements two rings together. 



* ' Science Gossip.' 



B 2 



