486 



♦ KNOWLEDGE 



[Dec. 12, 1884. 



porting it iu a frame, B, ia front of the eye-piece. A, of a 

 microscope. C, is a reflector or lens, from or through which 

 (according as it is one or the other) a beam of light is sent 

 through the object and then through the microscope into 

 a long bellows camera, E, where it falls upon a sensitised 



Fig. 1. 



plate in the dark slide, F, at the back of the camera. If 

 C be a double convex lens, a paraffin lamp placed to the 

 right will give all the light that is necessary for imparting 

 to the plate at F, an enlarged photographic image of the 

 object, B. The development and fixing of the negative 

 taken at F is a matter of ordinary photographic detail. 

 The myriads of interesting objects that might be thus easily 

 photographed cannot fail to impress one with the fact that 

 there is here alone sufficient recreation for many a long 

 and, perhaps, otherwise tedious winter evening. But 

 when the photographer wishes to display his work 

 to a large circle of friends simultaneously, either at 

 home or in the lecture-hall, what can be better or easier 

 than to adopt the plan illustrated in Fig. 2, where 



Fig. 2. 



a transparent slide, B, is placed in the lantern, and an 

 enlarged projection of the picture thrown on the screen 1 

 For large assemblies, lime light or electric light apparatus 

 IS necessary ; but for drawing-room audiences, one of 

 many good oil-lanterns (and their name is legion) will 

 answer every purpose, while a white window-blind will 

 serve admirably as a screen. Nor need the amateur go far 

 for his transparencies, provided he has a goodly store of 

 negatives. A transparent slide may be easily produced by 

 laying a sensitised plate over the negative (in a dark 

 chamber, of course), and then passing the pair of plates a 

 few times before an ordinary paraffin lamp. The sensitised 

 plate being lifted from the other, the picture may be 

 fixed in the ordinary manner. It is noticeable that these 

 transparencies are being very largely employed on the con- 

 tinent for the purpose of house decoration, windows, more 

 especially those on the staircases, being frequently glazed 

 with them ; and I fancy this is a practice which might be 

 adopted nearer home with a pretty and pleasing efl^'ect. 

 What I have thus far said is, I imagine, amply sufficient to 

 demonstrate how readily photography may be made to 



supply us with the means of pleasantly and profitably passing 

 our spare winter evenings. But photography in the present 

 sense of the word, that is to say the taking of negatives 

 during winter, is not altogether a species of Tom Tiddler'.s 

 ground. There are many views which the winter alone affisrds 

 — such, for example, as a snowstorm. It is, however, apparent 

 that in taking such a picture the work must be done 

 rapidly, or our flakes of snow will have rather the appear- 

 ance of icicles. Notwithstanding our comparatively poor 

 light in the colder period of the year, the number of rays 

 reflected by the snow is sufficient to imprint a picture in a 

 very brief space of time. The difficulty is rather to 

 adequately shorten the time during which the plate is 

 exposed. The obstacle is not, however, insurmountable. 

 Fig. 3 is a perspective view of what is at present the 

 best piece of apparatus devised (for ordinary purposes) 



Fig. 3. 



Fig. 4. 



for mechanically limiting the period of exposure. It is 

 known as an instantaneous shutter. A is a shutter which is 

 attached by its upper edge to the inner side of the brass 

 rod, J K. An elastic band attached at one end to the knot 

 or button H passes a little way round J K, and is then 

 attached by its other extremity to another little button 

 near the end J (not shown). E is a small brass stud on 

 the shutter A, aud it is held by means of the above- 

 mentioned spring against the little steel pin seen to pro- 

 trude from the cylinder C. A sectional view of this 

 cylinder is shown iu Fig. 4, where a b represents the 

 cylinder, /( an india-rubber tube connected with a pneu- 

 matic ball (F, Fig. 3) ; (/ is an air-tight piston which 

 slides up and down the cylinder ; e/ are two steel pins, 

 the former fitting closely to a hole in the fixed cap of the 

 cylinder, while ./" fits as closely to the screw-cap c cl. It 

 is evident that if the ball ( F, Fig. 3) be squeezed, air will 

 be forced into that part of the cylinder above g, and 

 will consequently force the piston downwards, which 

 will also carry with it the pin e. Bemoving the 

 pressure produces a partial vacuum in the ball, 



