( 365 ) 

 PROCEEDINaS OF THE SOCIETY. 



Annual Meeting of 9th Febkuart, 1881, at King's College, Strand, 

 W.C., The President (Dr. Beale, F.R.S.) in the Chair. 



The Minutes of the meeting of 12th January last were read and 

 confirmed, and were signed by the Chairman. 



The List of Donations (exclusive of exchanges and reprints) 

 received since the last meeting was submitted, and the thanks of the 

 Society given to the donors. 



From 

 Frey, H. — Das Mikroskop und die Mikroskopische Technik. 



458 pp. and 403 figs. 7th ed. (8vo. Leipzig, 1881) .. Tlie Author. 

 Diagram illustrating the Demonstration as to the Apertures ofl Mr. Crisp and 



Dry and Immersion Objectives / Mr. Stewart. 



Models illustrating the " Hemisphere Puzzle " in 2 forms . . Mr. Crisp. 



Mr. Crisp said that in the discussion on aperture, at the last 

 meeting, he had confined himself to pointing out that the photometrical 

 test on which the aperture question had then been rested was founded 

 on an entire mistake, for even assuming for the sake of argument 

 that such a test could properly be applied in the way and to the extent 

 propounded, the conclusion drawn was vitiated by the fact that the 

 radiation of light in air, water, and oil, was not identical, as supposed, 

 but varied as the squares of the refractive indices. 



It would, however, he thought, be advisable (having regard to the 

 reappearance at that meeting of some of the old fallacies which it was 

 supposed had died out) to have in the Journal a statement of the 

 leading points of the aperture question, not restricted to one aspect 

 only, but dealing with it in all its aspects. 



With this view he had prepared some notes, which would 

 appear in the next Journal (see p. 303), and he now laid before the 

 Society an enlarged copy of the diagram which accompanied the 

 demonstration that no dry objective could have so large an aperture 

 as an immersion objective of balsam-angle exceeding 82°. In the 

 face of this demonstration it was impossible to accept the invitations 

 that were at times made to see the apertures of objectives measured. 

 As well might they assist at a measurement of the three squares on 

 the sides of a right-angled triangle in support of the view that the 

 large square was not equal to the two smaller ones, in lieu of referring 

 the demonstrator to the 47th Prop, of the 1st Book of Euclid. 



With the diagram he also presented two glass " models " illus- 

 trating the " hemisphere puzzle," in remembrance of the most curious 

 error that had ever puzzled theoretical or practical microscopists. It 

 would be plainly seen that the hemispheres did magnify exactly 

 f times, and that the smaller one converted an inch objective into 

 a f inch, the latter utilizing, however, the same large diameter of the 

 back lens as the lower-power 1 inch. 



Ser. 2.— Vol. I. 2 C 



