February, igo5.] 



KNOWLEDGE & SCIENTIFIC NEWS. 



363 



theory on the subject, the President said that, in his 

 opinion, all these difficulties, anatomicaJ, physiological, 

 and physical, mig-ht be swept away by regarding each 

 facet as a little hole (possibly filled with a simple non- 

 refracting material). After dealing with various 

 points connected with this suggestion, the lecturer 

 went on to describe an experiment he had made which 

 seemed to support his contention very strongly. A 

 photograph of a piece of perforated zinc was made, so 

 \ery much reduced as to almost require a lens to see 

 the holes. This little artificial cornea was then placed 

 on a, microscope stage and a very small cross marked 

 on the mirror below. A slide then thrown on the 

 screen at once displayed the multiple image effect pro- 

 duced by these artificial means. 



A very interesting discussion followed the lecture. 



Gordon's Appa-ra-tus for Photo- 

 micrography. 



Many microscopists must have often desired some 

 simple form of photo^micrographic camera which could 

 be readily applied tO' a microscope, with little re-adjust- 

 ment, to obtain a photograph of some object which is 

 being examined visually. Mr. J. W. Gordon has de- 

 signed a small camera for this purpose, which, whilst 

 not differing in principle from other cameras of the 

 sort, such as that made by Mr. John Browning, con- 

 tains several original and useful features. Briefly, the 

 camera consists of a circular brass tube (A) about 



six inches long, which is placed over the microscope 

 C3epiece. At the upper end of the tube a small cap 

 (B C) contains a photographic plate, in size one 

 quarter of an ordinary lantern plate, i.e., i|-inch 

 squiu-e, giving circular pictures i|-inch in diameter. 

 Between this and the eyepiece is a projection lens 

 focussed upon the plate, and there is also a small ex- 

 posing shutter (D). Such a camera can be kept close 

 at hand during one's work, ready for use at any time. 

 If the observer's sight is normal, the photograph will 

 be sharp when the microscope is focussed for ordinary 

 vision, but as most people have some slight abnormali- 

 ties of vision, a duplicate tube (E), with a high-power 

 focussing eyepiece, is supplied. Tliis is first placed 

 on the microscope, in order to focus, and then merely 

 replaced by the camera. A small flange (F), fitted 

 over the upper end ol the microscope, forms a table 

 upon which to rest the camera. It has been found 

 that microscopes used in an upright position for photo- 

 micrography, have a tendency tO' move slightly down- 

 wards, and to prevent this a small metal block (G) is 

 provided, which fits above the coarse adjustment and 

 clamps the tube in any position. The principle of this 

 clamp is so simple thai one wonders it h:is not been 

 thought of before. It can be made to fit any micrcv- 



scope, and should be equally useful in preventing 

 broken slides at microscopical exhibitions. The whole 

 apparatus is noticeable for its extreme simplicity, 

 ease of adjustment, and moderate price, whilst the 

 two photographs reproduced herewith will show what 



Tongue of Blosvfly. 



Pleurosigma Formosum. 



the resulting photographs are like. 1 may add that 

 tliese photographs were taken with a Welsbach gas 

 lamp, and a yellow screen, with exposures varying 

 Irom 20 to 60 seconds. The apparatus is made bv 

 Messrs. R. and J. Beck, Ltd. 



Microscopic Shdes. 



Messrs. Clarke and Page, of 104-106, Leadenhall 

 Street, E.G., have sent me four very beautiful slides of 

 marine objects. The staining and mounting show the 

 structures to unusual advantage, and the prices are 

 moderate. Messrs. Clarke and Page bought the stock 

 of Mr. Jas. Hornell, which was, of course", limited, and 

 I understand that these slides are their own mountmg 

 to replace his stock. They have sent me, at the same 

 time, a catalogue of mounted slides, and if those I 

 have seen are representative, they have fully main- 

 tained the high standard set by Mr. Hornell. 



Notes arvd Queries. 



W. Bimll, Kilmarnock. — All slides mounted for examina- 

 tion by transmitted light, that is, all transparent slides, can be 

 readily shown upon a screen by means of a projection micro- 

 scope, and they will, of course, thus retain the'.r proper colours. 

 But, unfortunately, such a microscope is rather an expensive 

 apparatus, as the ordinary microscope is not suitable. A 

 lantern is needed with a po\yerful source of illumination; 

 nothing weaker than the oxy-hydrogcn light is any good, and 

 at a distance of more than a very few yards from the screen 

 the arc light becomes necessary. Even with this last powerful 

 light the ditficulties become serious with the higher magnifica- 

 tions given by immersion lenses, but the oxy-hydrogcn light 

 is quite satisfactory for moderate distances and moderate 

 powers. Then special parallelisers and condensers are 

 necessary to supplement the condenser of the lantern. The 

 microscope itself does not differ materially in principle from 

 an ordinary microscope except that its body-tube is neces- 

 sarily very short. I am afraid, therefore, your most economical 

 method would be to make lantern slides of the objects you wish 

 to show. You could, however, of course content yourself 

 with borrowing as many microscopes and lamps as possible, 

 and showing the slides after the reading of your paper. This 

 is commonly done at meetings. Hand-microscopes, which 

 can be handed round, are far from satisfactory. 



S. P. Miimmiiy, London, and E. J. Addcrley, Hull. — I regret 

 that owing to pressure on my space answers to your queries 

 must be held over for another month. 



[Communications and Enquiries on Microscopical mattirs should be 

 addressed to F. Shillington Scales, "Jersey," St. Barnabas Road, 

 Cambridge] 



