350 PROCEEDINGS OF THE 



ceeded, the speaker showed the effects of diffraction spectra under 

 varied conditions. In using annular illumination they were 

 using a number of central cones of illumination overlapping to 

 form the annular. He also pointed out the danger of using 

 annular illumination unless great care was exercised as to the 

 tube length. 



Mr. Blood said it was extremely easy to resolve diatoms with a 

 central stop in which case they were merely seeing the image of 

 the stop. In many objectives the central portion and the 

 extreme edge were over corrected, but the intermediate zone was 

 quite right. 



Mr. Brown said he had been examining Pinnularia nobilis for 

 the last forty years, and thought he had obtained a resolution of 

 it, but not the same as that described by Mr. O'Donohoe. For a 

 long time he was unable to get any resolution, but he believed he 

 had now done so, and hoped shortly to read a paper on the subject. 



Mr. Akehurst explained that the photographs shown in illus- 

 tration of his paper were taken to show the contrast between the 

 ordinary and the new method of illumination with central stop 

 below the condenser, but without cutting down the N.A. of the 

 objective. 



Votes of thanks were cordially passed to Mr. Akehurst and 

 Mr. O'Donohoe for their papers. 



In place of the usual monthly conversational meeting, a Conver- 

 sazione was held on February 10th, in the Great Hall, King's 

 College, by kind permission of the Principal. Nearly five hundred 

 members and visitors were present, and about 170 microscopes, 

 besides other apparatus, were on exhibition. It is not possible to 

 give a complete list of the objects shown ; but among others may 

 be mentioned a number of coloured drawings of water-mites, 

 including a series of fifteen figures illustrating the life-history of 

 Hydrachna ylobosa (de Geer), by C. D. Soar ; foraminifera under 

 microscopes, and material from the sea-bottom in various stages 

 of preparation, by Messrs. Heron-Allen and Earland ; living- 

 rotifers by Messrs. Bryce, Dunstall, Rousselet, Scourfield and 

 others ; stereophoto-micrographs by Messrs. A, E. Smith and 

 Taverner ; photomicrographic apparatus and some sixty natural- 

 colour lantern-slides by E. Cuzner ; some fine photomicrographs 

 in colour of polarised rock sections by Messrs. Cafiyn and Ogilvy. 



