PROCEEDINGS OF THE SOCIETY. 345 



Mr. Stewart called attention to two slides exhibited by Mr. 

 Dreyfus, one of which {Poteriodendron peiiolatiim) was one of the 

 remarkable flagellate Infusoria (figured in Stein's work), in the form 

 of a tree goblets of glass-like transparency, an outline of which he 

 drew on the board. It had been found in one of the ponds at the 

 Zoological Gardens. The other slide was a fungus {Gymnospor- 

 angium), one of the Uredinece. 



Mr. Crisp called attention to the fact of Messrs. Powell and Lea- 

 land having constructed a ^ oil-immersion objective, which they had 

 brought for exhibition. 



Professor Keith's " Note on Diagrams exhibiting the path of a ray 

 through Tolles' ^ Immersion Objective " was read by Mr. Crisp (see 

 p. 269 and Plate XII.) and the diagrams exhibited. The original 

 diagram copied on p. 143 of vol. i. and computation forming 

 Plate YII. of that volume were also shown. 



Mr. Wenliam's " Reply to Professor Keith's Note " (see p. 270) 

 was read (see p. 271). 



Mr. Crisp stated that the Council had come to the conclusion that 

 it was desirable to close the controversy on the aperture question, and 

 that, with the possible exception of a paper promised by Professor 

 Abbe, it was not intended to print any further communications on the 

 subject beyond those read this evening. 



Mr. Tolles' paper on " An Illuminating Traverse-Lens " was read 

 by Mr. Crisp, and the apparatus exhibited and illustrated on the black- 

 board. 



Dr. Edmunds said that homogeneous immersion was nothing less 

 than a new point of departure for high-power objectives — such lense-; 

 going as far beyond water lenses as these go beyond air lenses. The 

 enormous resolving power of homogeneous immersion lenses could 

 only be brought out by corresponding illumination. For such illu- 

 mination the immersion principle was indispensable. He had long 

 worked with immersion illuminators, and found them perfectly easy 

 to manage. A crown lens, half an inch in radius and in depth an 

 entire hemisphere minus the thickness of the slide, would, when con- 

 nected to the slide with oil, do almost everything in the way of 

 oblique illumination, and no Microscope was now complete without 

 such an accessory. The travelling plano-concave addendum of 

 Mr. Tolles, though very pretty in theory, was not, he thought, of much 

 use as a working tool. 



Dr. Hudson's " Note on Mr. Deby's paper " (as to the identity of 

 Pedalion Hudson and Hexartlira Schmarda— see p. Ill) was read by 

 Mr. Crisp, and the two comparative drawings made by Dr. Hudson 

 enlarged on the board by Mr. Stewart. 



