540 PROCEEDINGS OF THE SOCIETY. 



Mr. Conrady gave a resume of his second paper on " Theories of 

 Microscopical Vision," in which he applied to perforation-patterns and 

 to crossed lines the principles laid down in his first paper on the subject, 

 his aim being to show that the gradual improvement of images with 

 increasing aperture could be fully accounted for by the Abbe theory. 

 He also claimed that the employment of wide " aplanatic " cones of illu- 

 mination was amply justified by this theory, because, on the one hand, 

 it protected the observer against spurious images due to a defective 

 objective or bad adjustments, simply because only a perfectly adjusted 

 instrument would bear a wide cone ; whilst, on the other hand, the wide 

 cone gave the full resolving power of the instrument in all directions, 

 thus disclosing at one glance all that a given instrument could show. 



He also adduced experimental evidence which would seem to dis- 

 prove the spurious disk theory, whilst upholding the diffraction theory. 

 Experiments illustrating this were shown under Microscopes in the room. 



In moving a vote of thanks to Mr. Conrady, the Chairman said the 

 Society was greatly indebted to him for his papers on this subject, which, 

 to be fully appreciated, must of course be read. 



An exhibition was then given of a number of lantern slides prepared 

 by Mr. Flatters from plates illustrating beautiful microscopic objects 

 from amongst the Radiolaria, Foraminifera, Infusoria, Desmids, etc. 

 Some extremely fine lantern photographs of corals, from Mr. W. S. Kent's 

 work on the Great Barrier Reef of Australia, were deservedly admired, 

 and the thanks of the Society were heartily accorded to Mr. Flatters for 

 the opportunity afforded to the Fellows of seeing these excellent repro- 

 ductions. 



Notice was given that the rooms of the Society would be closed on 

 and from August 14th to September 11th. 



The following Instruments, Objects, etc., were exhibited : — 



The Society : — Pocket Botanical and Universal Microscope, by W. & S. 

 Jones ; a Wilson's Screw-barrel Microscope, probably by Adams ; an Old 

 Portable Microscope, by Shuttleworth ; Lantern Slides, mostly zoological, 

 lent for the occasion by Mr. Flatters. 



Mr. A. E. Conrady : — -Phurosiyma angulation, just resolved with 

 N.A. 0*55 and a full cone of illumination; ditto, with J in. objective, 

 N.A. 0*65, having spherical aberration, the broken edge focussing at a 

 different level compared with the structure ; diffraction spectra, with 

 curved wave-fronts (no change whatever takes place on racking the 

 condenser up and down, although the wave-fronts change from concave 

 to convex) ; diagrams shown on the screen in illustration of his paper. 



Mr. C. L. dirties : — Apparatus for obtaining dark-ground illumina- 

 tion with high powers. 



Dr. W. S. Lazarus-Barlow : — A warm stage, heated by gas or oil 

 flame. 



Mr. Cecil R. C. Lyster : — An electrically heated warm stage. 



Mr. Rheinberg : — The production of achromatic interference fringes. 



Mr. Rousselet : — PI umatella punctata, received from Mr. John Hood. 



