441 



Mr. E. M. Nelson exhibited and described an achromatic 

 bull's-eye condenser, which would be also found perfectly apla- 

 natic. Also a new 10-power loup, the object of which had 

 been to obtain a greater length of focus than in the previous 

 form of the same power. In this case the focal length was T 8 <j-" ; 

 in construction the lens was a triplet, but the curves were not 

 symmetrical. Mr. Nelson also read a short note on diatom 

 structure, and exhibited a very much amplified photomicrograph 

 of a portion of a diatom, which he said was on the scale of 

 1 postage stamp = 3i acres. 



Dr. Tatham said that on his way down to the meeting he 

 called on Mr. Nelson, and had the pleasure of finding him at 

 work on high-power definition. He said to him, " Just look at 

 this carefully, and you ought to see the fine perforated membrane 

 of the secondary structure." He did look for a long time, and was 

 successful in glimpsing this structure ; but, although he saw it, 

 he did not take any credit to himself for so doing : the reason 

 was the excellence of the arrangements made — for Mr. Nelson 

 was working apochromatically from end to end, and eyepiece 

 and lens were in perfect conditions of adjustment, and it so 

 happened that he was at the right end of the tube at the right 

 time to see this, and to be quite sure that it was a reality. They 

 were working with the full aperture of Powell's apochromatic 

 condenser, and the structure which he saw, he was glad to say, 

 was unquestionably seen also by Mr. Nelson himself. He re- 

 garded this as one of the most beautiful sights he had experienced' 

 since he became a microscopist. 



The thanks of the meeting were voted to Mr. Nelson for his 

 communications. 



The Secretary announced that there would be no ordinary 

 meeting of the Club in April, as the third Friday would be 

 Good Friday. He also reminded the members of the Conver- 

 sazione fixed for May 4th, and expressed a hope that they would 

 do their best to make it a success, worthy of the Club. 



Asplanchna priodonta ... ... ... Mr. J. M. Allen, 



Euchlanis diletata ... ... ... ... Mr. W. Burton. 



Coryne vaginata ... ... ... ... Mr. G. T. Harris. 



Eye of a butterfly ... ... ... ... Mr. J. Rheinberg. 



Proales wemecki in galls of Vaucheria . . . Mr. C. F. Rousselet. 



