THE president's ADDRESS. 363 



by the insertion of the card. So difficult is this operation with 

 a bellows camera that telescopes and opera glasses have been 

 employed for the examination of the image at the far end, but 

 the card and the moveable tubes render this quite unnecessary. 



It is now necessary to explain the method of working this 

 apparatus, and to point out the reasons for its special design, 

 noticing especially where it most differs from the usual type of 

 apparatus. The main points of difference are two in number: 

 — 1st, the absence of what is known as the turn out, and, 2ndly, 

 the non-fixit}' of camera. With regard to these two points 

 there are two photographic axioms to which your attention 

 might be drawn. The first is that the photographic bench is 

 not the proper place for microscopic observational Avork. 

 In other words, the object about to be photographed should 

 have been examined, the corrections of the objective, the size 

 of the cone of illumination, and all the data necessary for the 

 production of a critical image learnt before the object is 

 brought to the photographic bench. 



Further than this, if the critical image has been obtained 

 by using a number eight diaphragm, it is necessary to hammer 

 away at the photographic part until a successful negative has 

 been obtained with that same diaphragm, for it is so easy to 

 substitute a diaphragm two sizes smaller, and thus secure 

 contrast. When once the object has been learnt, and the 

 corrections, etc., are known, it is neither a difficult nor a 

 long matter to reproduce the critical image on the photo- 

 micrographic bench. It is therefore quite unnecessary to 

 turn out the microscope ; and, secondly, the standing, and 

 not the sitting, posture is the correct one for the photo- 

 micrographer to adopt. While on this subject it might 

 be pointed out that vibration, a spectre which for long has 

 haunted photomicrographers, myself included, is in practice 

 found to be a myth. If there is a microscope in the world 

 more likely to be influenced by vibration than any other it is 

 Powell's No. 1, for it has a long body and a long bar move- 

 ment ; nevertheless, during all the years it has been in use not 

 a single negative has been lost through vibration, and, what is 

 more, I never heard of anyone else losing one from that cause. 



This being the case, how much less likely is a crane arm 

 microscope to be affected by vibration ? But so powerful has 



