388 PHOTOGRAPHING MINUTE OBJECTS 



have some that it would be difficult to beat as regards defining 

 power and the amount of light that they pass. For micrographic 

 work it is an immense advantage to have more light than you want, 

 as it can always be stopped down by the use of the iris diaphragm, 

 or as some prefer a set of stops, these perhaps, in many cases, have 

 an advantage. I think it is well never to use a higher power than 

 you can help ; it is better to get the amount of magnification by 

 extending the camera, and put in an ocular or compensating eye- 

 piece ; these are made on purpose, and work with a spiral motion 

 to the eye-lens, so as to focus the diaphragm stop in the tube. A 

 simple form of apparatus I have designed and will show you a 

 slide of presently. The camera is of long extension, and has a 

 bellows 30 in. long ; the front part is made to rack back, so as to 

 clear the eye-piece of the microscope, to enable the operator to 

 revolve the instrument on its centre. The microscope is one of 

 a new series of stands Messrs. Newton have recently brought out, 

 and for all ordinary work will answer every purpose ; it has a 

 simple mechanical substage, fitted with an iris diaphragm and 

 Abbe condenser, with adjustments for centering ; the mirror is 

 made to swing out of the way when not in use. 



A very convenient way of seeing how to arrange the object is 

 to place a flat mirror at some distance from the ground glass at 

 the end of the camera ; the image on the screen is reflected on 

 to it. You can by this means see that the object is in the centre 

 of the field, and easily focus the object and centre the light ; in 

 fact, you can, without any difficulty, get the whole thing ready in 

 a short time, except the final focussing, which has to be done very 

 carefully. Having now roughly focussed the object, remove the 

 ground-glass screen, insert a plate of plate-glass with lines ruled 

 on it, and it will be found useful to have these lines ruled at a 

 given distance apart, say one-tenth of an inch, and a Ramsden 

 eye-piece used for focussing aerial images; coloured screens or light 

 filters are very useful. It is well to be provided with several differ- 

 ent ones, such as signal green, bluish grey, and yellow, and a few 

 cells fitted with coloured fluids, for, in many cases, working in 

 monochromatic and coloured light, according to the object to be 

 photographed, is necessary. I had intended to show you a num- 

 ber of photographs taken with various screens, but have not had 



