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Club in 1877, and for some time held office as a vice- 

 president. 



The Hon. Secretary read a note communicated by Mr. E. M. 

 Nelson, F.R.M.S., on "A New Semi-Apochromatic i" The- 

 writer asked to be allowed to bring to the notice of the Club 

 a new form of objective, computed by Mr. A. E. Conrady, 

 F.R.M.S., and made by Messrs. Watson & Sons. It is a 

 semi-apochromatic -J-, of N.A. 0"74. The point of novelty about 

 the lens is the very great working distance it possesses — viz., 

 1 mm. An examination of this lens showed that its initial 

 power was 60, and that its aperture was correctly stated. Its 

 performance upon the usual test objects was highly satisfactory, 

 which proved that not only was the objective well corrected, 

 but that it also had its lenses truly centred. Various biological 

 objects were examined, including sections of animal and vegetable 

 tissues, entomological preparations, and geological and mineral 

 substances, all of which were brilliantly shown. Bacteria were 

 then examined under very deep eyepieces, and the images given 

 by the lens were not in the least broken down. The flagella 

 of the tubercle bacillus were seen. The image, naturally, was 

 a difficult one, but not exceptionally so. As to the working 

 distance of the lens, it focussed an object through a slip 064 in. 

 thick. An objective such as this cannot but be useful to many 

 of the members of this Club, who are so well known for their 

 critical examination of pond life, where a long working distance 

 is a sine qua non. 



The President said that he should not have made any remark 

 upon this objective had not Mr. Nelson brought the matter 

 forward ; but as he had had the privilege of seeing and testing 

 it when in its workshop mount, he felt he might add his testi- 

 mony to its excellence. Mr. Nelson had not mentioned its 

 behaviour with the Abbe test-plate ; but he might add that 

 the correction of the outer zone, so difficult to deal with, was 

 decidedly an advance. He could honestly endorse every remark 

 made by Mr. Nelson, and, in point of fact, he was quite unable 

 to break down the image. Its aperture was sufficient for all 

 practical purposes, and its working distance was 1 mm., as 

 stated. He felt that he must be allowed to congratulate 

 Mr. Conrady on his computations, and Messrs. Watson & Sons 

 on their manufacture of the combination. 



