248 



SCIENCE-GOSSIP. 



Mr. R. G. Mason's Catalogue. — Mr. R. G. 

 Mason, of 69, Clapham Park Road, sends us an 

 interesting list, which contains several novelties, 

 amongst which we may mention a convertible lantern 

 and table microscope. Most of the microscopes 

 appear to be of good design, and there is a new model 

 specially designed for the use of teachers, which is 

 •called " The Champion," concerning which we can 

 speak favourably after a personal inspection. It is on 

 a tripod form of foot, has diagonal rack coarse adjust- 

 ment, and lever fine adjustment, draw-tube, sub-stage 

 tube for condenser, and the usual mirrors. The work- 

 manship is sound and the price of the stand alone is 

 only £2, 13s. 6d. We may also call attention to Mr. 

 Mason's sets of mounted slides for students, and lantern 

 slides for lecturers, specimens of which have been 

 submitted to us, and which are both good and reason- 

 able in price. Beginners will find the various series of 

 prepared but unmounted objects excellent practice, and 

 we note with approbation that these have been, in 

 each case, sent out still moist from the final clearing 

 stage — a manifest improvement on the usual dried 

 objects sold for this purpose. Mr. Mason also sells 

 an unostentatious, but practical, little sixpenny 

 pamphlet on elementary mounting, which should 

 have a good sale. 



Cement for Glycerine Mounts. — 

 In making permanent specimens of objects 

 mounted in glycerine or Farrant's medium, 

 considerable difficulty is experienced in 

 cementing the cell. I have tried various 

 methods, but the most successful in my 

 hands has been to use a thick solution of 

 gum dammar in benzole. Select a clean 

 sample of the gum and dissolve in 

 benzole until the required consistency is 

 reached. The edge of the cover glass is then freed 

 from superfluous mountant, and the cement laid on in 

 the usual way. The first layer will in a few hours be 

 sufficiently set for the application of a second, which 

 is generally necessary. — Frederick Noad Clark, 

 Paddington Infirmary, London, W. 



ANSWERS TO CORRESPONDENTS. 

 Mounting Algae. W. H. B. (Folkestone). — You 

 have, unfortunately, made your first attempt on a 

 ■difficult subject. I would suggest boiling some water 

 for ten minutes to get rid of the air in it, and in this 

 gently heating or even boiling the specimen itself, 

 for other ten or fifteen minutes, and finally putting 

 the latter under the air pump in a small quantity of 

 the same water. Before mounting in glycerine jelly, 

 soak in a mixture of glycerine and water, and 

 examine under a dissecting lens. If any air-bubbles 

 should still remain in the cells they must be removed 

 carefully one by one with a fine needle. It was 

 useless putting the slide under the air-pump when 

 mounted — glycerine jelly sets and cools too quickly, 

 and is besides too dense to displace the air in the 

 cells. The object needs the above careful prepara- 

 tion beforehand. Glycerine jelly is always more 

 troublesome than Canada balsam with respect to air 

 bubbles, but is otherwise very suitable for botanical 

 mounting. There is no book which will enable you to 

 identify algae off-hand, without a preliminary study of 

 the subject, but I would suggest your obtaining 

 "Gray's British Seaweeds" (10s. 6d.), or Harvey's 

 "Manual of British Marine Algae" (21s.). The 

 authoritative book on Marine Algae is Harvey's 

 " Phycologia Britannica," but it is very costly 

 (£j 10s). M. C. Cooke's " British Freshwater 

 Algae " {£4 10s.) is the best book on the sister 

 subject. 



MICROSCOPY FOR BEGINNERS. 



Bv F, Shillington Scales, F.R.M.S. 



( Continued from jtage 215. ) 



Into the multitude of accessories figured and 

 described in microscope-makers' catalogues we cannot 

 of course enter in these papers. One or two items, 

 however, are sooner or later necessary. For instance, 

 some method of measuring objects will be required, 

 and the simplest means of doing this is to become 

 possessed of a stage miciometer, which is a slide 



Stage Micrometer. 



3in. by iin. , ruled in rwlhs and -[-oVitths of an inch, 

 or ^ths and TTnjths of a millimetre, and costing 5s. 

 A small disc drops into the Huygeniari eyepiece, and 

 lies on the diaphragm. This is called the eyepiece 

 micrometer, and it is also ruled with divisions that 



SWIFT 8< SON 



LONDON 



Eye-piece Micrometer. 



generally bear some relation to an inch or millimetre 

 scale. This also costs 5s. To make measurements 

 it is only necessary to note the number of arbitrary 

 divisions in the eyepiece micrometer corresponding 

 with the object to be measured, and then to replace 

 this object on the stage by the stage micrometer, and 



Nose Piece. 



note the exact measurements which correspond to those 

 taken in the eyepiece. There are other forms of micro- 

 meter, but the above is simple and inexpensive, 

 and quite satisfactory for most purposes. A nose- 

 piece is a great convenience, but scarcely a necessity. 

 One or two opticians have .latterly so arranged their 

 objectives that they are all nearly in focus when 

 rotated on the nose-piece. Under any circumstances, 

 however, we do not recommend the use of a triple 

 nosepiece, to say nothing of a quadruple one, as the 

 weight of three objectives is quite sufficient to put a 

 severe strain upon the fine adjustment. The cost of 

 a double nosepiece varies from ios. 6d. upwards. _ 



It is quite practicable to make good drawings direct 

 from the microscope when used in the ordinary way, 

 the paper being placed as near the stand as possible, 

 but for accurate work, some form of camera-lucida is 

 necessary. 



