ON PHOTO-MICROGRAPHY. 183 



use of the eyepiece the advantage is gained that any 

 ordinary camera may be used, and in consequence 

 of the shortness of the distance between the 

 focussing screen and the microscope, the various 

 adjustments of the latter are accessible, while 

 focussing, without any special arrangements. In 

 order to secure the same amount of magnification 

 or to cover the same sized plate, when the eye- 

 piece is not used, the camera must be of special 

 construction so as to be capable of extension to two 

 or three times the former distance, and when so 

 extended to say a yard the focussing screen can 

 only be reached by rods and bands or intermediate 

 gearing. For facility, therefore, the eyepiece 

 method is commendable, but the impairment of 

 the image and the loss of light due to the inter- 

 position of two additional un corrected lenses are 

 so considerable that we would advise the removal 

 of the eyepiece for all but special purposes, such 

 as the covering of a very large plate. 



The microscope may be of any ordinary construc- 

 tion that will allow the body to be placed hori- 

 zontally, and it should have a stop to prevent it 

 going beyond that position. It should be provided 

 with a coarse adjustment, by rack and pinion, and 

 a very sensitive fine adjustment for slow focussing. 

 Very much of the success of the work depends upon 

 the excellence of the slow motion. It is always a 

 very important part of the microscope, but for 

 photo-micrography it becomes especially so. It 

 should be free from the slightest lateral motion, 

 lest, in focussing, the image be removed from the 

 centre of the plate, a very small displacement of 

 the object glass being sufficient to effect this, when 



