HARDWICKE'S SCIENCE-GOSSIP. 



J 93 



ON DRAWING MICROSCOPIC OBJECTS. 



By BERNARD HOBSON. 



PLANNED the 



apparatus about 

 to be described 

 without previous- 

 ly knowing of 

 similar inventions, 

 such as that of 

 Mr. C. W. Cooke, 

 mentioned in 

 Beale's book, 

 page 2S, or that 

 of Mr. Morrison, 

 mentioned in the 

 American Month- 

 ly Microscopical 

 Journal for 18S2, 

 page 59- 



Drawing by 

 this " micro- 

 graphic camera " 

 is the simplest, 

 cheapest, most convenient, and at the same time, 

 not at all a bad, although, perhaps, not the best, 

 method of delineating objects. The camera consists 

 of a Huntley & Palmer's large square-shaped tin 

 biscuit canister, measuring oi X 8£ X 92 in. deep. In 

 the centre of the lid I have had a circular hole 5 \ in. 

 diameter cut, and a similar hole z\ in. at the bottom of 

 the canister. In the hole at the bottom a conical tube, 

 2^ in. long X 2 in. greatest X \\ in. least diameter, is 

 soldered. The paper being stripped off the canister 

 and the whole being japanned black, it presents 

 a neat appearance. Inside the canister a piece of 

 plate-glass, 8}| x 8§ in. fits underneath the lid, 

 but rests on the top edges of the canister, and is 

 held firmly in position by the lid, when the canister 

 is shut. A piece about 5^ in. square of the thinnest, 

 whitest tracing paper obtainable is inserted between 

 the lid and the plate glass, which hold it in position 

 opposite the large central hole. The whole of the 

 camera is painted dead-black inside, with lamp- 

 black and turpentine. Cost as follows : 

 No. 225. — September 1883. 



Canister ......... 1 



Japanning, cutting holes, soldering tube on, cutting 

 circular plate mentioned below . . . .2 



Plate glass . o 



d. 

 o 



o 



4 



Total 



3 4 



I intended to use the above-mentioned apparatus 

 with eye-piece of the microscope, arranging the 

 tracing-paper to be at ten inches, the fixed distance 

 of distinct vision, from the eye-piece, but found that 

 when the light brought to focus at a point was 

 diffused over a circle of 5f in. diameter the loss of 

 definition was too great. By taking off the eye-piece 

 far better results are obtained. The conical tube of 

 the camera is then slipped over the microscope tube, 

 after having first focussed the object .with the eye- 

 piece. If the illumination be strong enough, and all 

 light be excluded from the top of the camera, where 

 the tracing-paper is, an image of the object will be 

 thrown on the tracing-paper. To bring it to focus, the 

 coarse-adjustment milled-head must be turned ; then, 

 by moving the object and the light, the image may 

 be made to occupy the centre of the field, and the 

 centre of the circle of light projected on the tracing- 

 paper. For convenience in drawing it is better to 

 incline the microscope at the usual angle, and sup- 

 port the camera above it at the same angle. I make 

 use of a small wooden camp-stool, with a fiat wooden 

 top, and insert books or two oblong iron seven-pound 

 weights under the camera to prop it up at the right 

 inclination. If any light enters between the tube of 

 the camera, and that of the microscope, it may be 

 completely excluded by using an india-rubber cone 

 (used by plumbers for connecting wash-basin pipes), 

 price &d., made like a funnel, and open at both ends. 

 This serves to make a light tight connection between 

 the two tubes. It is convenient to have a circular 

 plate of tin japanned on the outside, and blackened 

 on the inside surface to fit into the large circular hole 

 in the camera. In this plate a much smaller round 

 hole is cut. This enables one to vary the size of the 

 field of view, and centre the image if required. 



I saw in a book called the " Minor Arts," by 



K 



