440 



the stops suggested, and the improved general definition of the 

 image in the former case was very noticeable. Besides several 

 large diagrams, by the help of which the paper was explained, 

 special photo-micrographs by Mr. Taverner served to illustrate 

 various points dealt with. 



Owing to the lateness of the hour, discussion was deferred to 

 the next meeting, and, after votes of thanks to the authors of the 

 various papers, the meeting was adjourned. 



At the meeting of the Club held on May 18th, Dr. E. J. Spitta, 

 F.R.A.S., F.R.M.S , President, in the Chair, the minutes of the 

 meeting held on April 20th were read and confirmed. 



Messrs. E. Ayerst Da vies, G. Churchouse, W. Martin, J. I. 

 Pigg, F.H.M.S., and E. Cuzner were balloted for and duly elected 

 members of the Club. 



Dr. Eugene Penard, of the University of Geneva, was 

 nominated by the Committee to fill a vacancy in the list of 

 Honorary Members. 



Mr. A. E. Smith read a note on " Stereo-photo-micrography," 

 exhibiting a number of very effective stereo-photo-micrographs 

 obtained by the methods described, ranging from low-power work 

 of 10 diameters up to 1,500 diameters — the highest power 

 successfully used. 



Mr. Conrady, referring to Mr. Rheinberg's paper read at 

 the previous meeting, said that he would like to make a 

 few remarks on a peculiarity of microscopical images which 

 Mr. Itheinberg had mentioned — viz. that when two objects of 

 exactly the same size were placed at different distances from the 

 object-glass (but within range of its " depth of focus "), the more 

 distant one was not always depicted as the smaller, but did 

 sometimes actually yield the larger image. The explanation of 

 this strange anomaly was to be found in Professor Abbe's theory 

 of the " iris" and " pupils " of optical systems. 



As a rule there was in every optical system one aperture which 

 limited the diameter of the cones of rays which were allowed to 

 pass from any point in the object to the conjugate point in the 

 image. Thus, in photographic lenses, the iris-diaphragm re- 

 presented this limiting aperture, whilst in microscope-objectives it 

 was usually formed by the shoulder against which one of the 



