89 



November 16th, 1900. — Ordinary Meeting. 



Dr. J. Tatham, Vice-President, in the Chair. 



The minutes of the preceding meeting were read and confirmed. 



The following gentlemen were balloted for and duly elected 

 members of the Club :— Mr. J. F. Allcock, Mr. S. G. S. Dicker. 

 Mr. S. E. Dowdy, Mr. C. W. Marshall, Mr. G. H. J. Kogevs, 

 Mr. B. J. Vernon, F.R.C.S. 



The additions to the library since the last meeting were 

 announced. 



Mr. Merlin's paper " On the Resolution of Amjjhijyieicra 

 2)eUucida, etc., with a Dry Lens and Axial Illumination," was, in 

 the absence of the author, read by Dr. Spitta. 



Dr. Spitta said that the paper just read was probably of even 

 more interest for its surrounding considerations than for the 

 actual facts contained in it. The explanation of the whole 

 matter was, it appeared to him, that the specimen used ivas 

 coarsehj marked, as indeed some undoubtedly were. Before 

 proceeding to show why he took this view, however, he begged 

 members to understand that in making his remarks he did not 

 wish to express any doubts as to the veracity of Mr. Merlin's 

 statements. But he believed that what he had to say offered an 

 explanation which had possibly escaped the author's attention. 



To enable an object consisting of lines separated by minute 

 intervals, or dots, or any small structures, to be seen, two 

 conditions were absolutely necessary. First, that such objects 

 should be sufficiently magnified for the eye to be capable of 

 seeing them ; and secondly, that the N.A. of the objectiv^e should 

 be high enough to render such objects sufiiciently resolved ; for 

 every one in the room was familiar with the fact that mere 

 magnification without sufficient N.A., or " emj)ty magnification," 

 as Professor Abbe called it, was as useless as N.A. Avithout the 

 proper amount of magnification. 



Now with regard to the first condition. It was supposed that 

 2^0- inch represented the minimum distance that two objects, 

 whether lines or dots, must be separated for the normal human 

 eye to see and separate them distinctly at a distance of ten 

 inches. No lines or dots closer than this could be recognised 



