397 



that if the cover were made with sloping flaps a reduction in size could be 

 effected without altering the capacity. 



Mr. Karop thought the members of the Club who heard a paper read there 

 some time ago by Mr. Underhill, upon "Spiders," would be glad to know 

 that it was now published in the " Journal of the Postal Microscopical 

 Society." 



The President read a paper " On Diffraction Phenomena," the subject 

 being freely illustrated by drawings on the black-board. 



Mr. Ingpen regarded the President's paper as a valuable contribution to 

 the literature relating to those optical principles the knowledge of which 

 was essential to microscopists, and he hoped that it would be followed by 

 others treating in a simple manner other branches of the subject upon 

 which erroneous views still existed. Most of the more valuable treatises, such 

 as those by Professor Abbe and the late Dr. Fripp, were in a rather technical 

 and abstruse form. This partly accounted for the reluctance shown 

 by some of our best workers to adopt the most important theories of micro- 

 scopical vision ; preferring to draw their own conclusions from what they 

 saw. 



Mr. E. M. Nelson said he had listened to the paper with grpat pleasure, 

 and he believed they would nowhere find a more clear and concise descrip- 

 tion of interference phenomena than had been given to them by the President 

 that evening. He hoped Mr. Ingpen's words would come true as to its 

 leading to the production of a treatise on the subject in some simple form ; 

 indeed, he thought they were a lucky Society to get such a paper as they 

 had just heard. It had dealt with the subject so fully that he felt he could 

 add nothing to it ; every point seemed to have been touched. As, however, 

 his name had been mentioned, he might say that he was very glad that he 

 had been the means of bringing it forward. Several members had talked 

 to him about the subject of diffraction phenomena, and for that reason he 

 thought he would bring a very simple description of them before the Club, 

 and without pretending to produce anything like a full or perfect treatise 

 upon the point, he took up the subject of diffraction with regard to diatom 

 structure. If he had accepted the advice given by the Royal Microscopical 

 Society he should have given up the study altogether, but he had not done 

 so, and as a consequence he had derived a great deal of pleasure and profit 

 from the study, finding that, though they could not, perhaps, pick up all 

 the diffraction spectra, they could at any rate do a good deal. "When look- 

 ing at a specimen such as those he had frequently shown in that room, 

 where the structure was shown to be irregular and not uniform, it was 

 impossible to believe that the appearance seen was due to diffraction 

 phenomena, which always tended to produce pictures with a regular 

 pattern. 



Mr. T. F. Smith said he could only express the delight which he felt on 

 hearing this paper, which he thought would remove a great many dis- 

 couragements from the way of those who generally got pushed aside as 

 recording nothing but diffraction defects. He thought that to believe in a 

 theory was one thing, but to believe in the application of it was another, 



