532 



Mr. Stevens had sent three mounts for the Club's cabinet, and 

 one of these, exhibited by Mr. Kousselet, showed very clearly the 

 principal points described. 



Mr. Kousselet said that at the last meeting of the Royal 

 Microscopical Society Mr. Siddall, of Chester, exhibited some 

 living diatoms which he said had radiate pseudopodia. He had 

 some of Mr. Siddall's material, and exhibited, under dark-ground 

 illumination, some of the specimens referred to. 



Mr. D. J. Scourfield thought the processes were not proto- 

 plasmic, but possibly siliceous. After two days' watching he 

 had found they occupied precisely the same position all the 

 time. They were not affected by nitric acid or alcohol. In 

 appearance they certainly resembled the radiate pseudopodia 

 of Heliozoa. 



Prof. Minchin said that it was quite a revolutionary idea to 

 record diatoms with pseudopodia ; but, especially after what 

 Mr. Scourfield had said, he thought it hardly likely that they 

 were really pseudopodia. If they were it should be possible to 

 observe, with high power, the usual streaming movements. But 

 -even if these processes were pseudopodia they would not account 

 for the movements of diatoms. 



Dr. Duncan J. Keid read a paper dealing with " Critical 

 Illumination in Visual Work with the Microscope." 



The subject was treated under the following heads : (1) The 

 Most Suitable Light ; (2) Collecting Lenses ; (3) The Principles 

 of Correct Illumination : (A) As regards the Field, (B) Filling of 

 the Objective with Light ; (4) Condensers ; (5) Distance of Lamp 

 from Substage Mirror ; (6) Critical and Non-critical Illumination; 

 {7) Working Aperture ; (8) General Arrangement of Light and 

 Apparatus in High, Medium and Low-power Work. 



Dr. Spitta said he congratulated Dr. Reid upon the neat way 

 in which he had placed the subject before them, and had nothing 

 to add to what had already been said. He quite agreed that 

 illumination with low powers was dithcidt, but whereas Dr. Beid 

 recommended oil lamps, he could only say that he abhorred 

 them, the electric light or limelight requiring so much shorter 

 exposure in photographing objects. 



Mr. Stokes said as regarded the use of the bull's-eye he did not 

 think that it was at all necessary, as it never improved anything, 

 ^nel although it gave a larger field of light personally he thought 



