PROCEEDINGS OF TIIE SOCIETY. 527 



meant that a longer exposure would bo required to get the same effect. 

 He had not done anything himself with a greater amplification than 

 X 200, but up to that magnification he had not found a want of light 

 to present any difficulty, in fact, he thought the mistake most often 

 made was that of having too much light thrown into the objective. In 

 practice he found it frequently necessary to cut off some of the light in 

 order to prevent the details of the picture from being blurred by too 

 much glare. 



Mr. J. Mayall. jnn., said he had made a great many experiments in 

 this direction with high powers from / 200 up to x 1000 or more, and 

 he might say that his experience went to show that the difficulty of 

 getting good result- with high magnifications direct from the object was 

 considerable, especially where a long exposure was required. In such 

 cases the risk of vibration was so great that very few photographs taken 

 in that way were successful. Even Dr. Woodward, who had such pre- 

 cautions taken as concrete floors to his workroom, frequently experienced 

 the difficulty arising from this cause. Mr. Mayall also referred to 

 instances of the improper use of the condenser, which was either not 

 placed correctly, or not centered, or the light was not properly focused ; 

 whereas to produce good results the object must be evenly illuminated. 



The Chairman said that few persons were so well able to give an 

 authoritative opinion on this subject as Mr. Mayall, so that they were 

 much interested to hear the remarks which had fallen from him. As 

 regarded high-power work, there could be no doubt that the centering 

 of the condenser was a very important consideration, but he thought it 

 was possible that where an object was photographed under a low p 

 there might be some advantage indirectly gained by an unequal illumina- 

 tion, and that appearances would result which might help them in some 

 way to form an estimate of the real form. It might in reality be an 

 imperfection, but it might, notwithstanding, have some practical utility. 



Mr. Mayall said doubtless every kind of illumination might be said 

 to contribute more or less to the accurate interpretation of images seen 

 in the Microscope. In cases, however, where an unequal illumination 

 was thought desirable, there were recognized methods of obtaining such 

 illumination. There were central stops, and a great variety of movable 

 stops, that could be used at pleasure either alone or in combination with 

 diaphragms of different sizes ; the employment of such means was most 

 important to enable the observer to interpret structure, especially, too, 

 as he could record exactly the method employed, so that his results could 

 be repeated by himself or others. But the unequal illumination which 

 he observed in a great many photomicrographs submitted to the Society 

 was due to imperfect adjustment of the condenser, imperfect adjustment 

 due in most cases to want of training in the skilful employment of the 

 Microscope and accessory apparatus. Such unequal illumination of the 

 field of the Microscope was, for the most part, not an effect deliberately 

 sought for by the microscopist, but was obtained hap-hazard, without 

 any systematic manipulation capable of being recorded and repeated. 

 It was this unskilful microscopy which he hoped to see remedied ; for 

 when it came to be combined with inferior technical photography, which 

 he regretted to say was far too often the case, then the results were by 

 no means admirable. It should surely be an essential part of the train- 

 ing of a microscopist to be able to centre and otherwise adjust his con- 

 denser and regulate the illumination ; such matters were the ABC of 



