1088 PROCEEDINGS OF THE SOCIETY. 



at present constructed, but might easily be made to do so, and thus to 

 answer the purpose of a rotating stage. 



Mr. John May all, jun., described the ToUes-Blackham Micro- 

 scope, exhibited by Mr. Crisp (see p. 520), and described and exhibited 

 Hyde's Illuminator, which had been devised to produce a luminous 

 field similar to that obtained by Mr. Wenham's reflex illuminator. 



Mr. Crisp called attention to several new applications of ebonite 

 to microscopical purposes, including " Botterill's Life Trough " (see 

 p. 148), now made in ebonite, Atwood's rubber-cell (see p. 1041), and 

 Beck's rotating holder for the latter. 



Mr. Swift exhibited and explained by means of a diagram a form 

 of (" calotte ") diaphragm which he had devised for bringing a series 

 of apertures immediately below the object (see p. 1053). 



Mr. W. G. Lettsom described Professor Abbe's new form of 

 binocular eye-piece (" Stereoscopic Ocular ") specially adapted for the 

 short-bodied instruments in ordinary use on the Continent, illus- 

 trating it by a diagram drawn upon the black board, and by the 

 exhibition of the instrument in the room. 



Mr. Crisp exhibited for comparison three other forms of binocular 

 eye-pieces, viz. those of Prazmowski, ToUes, and Verick. 



Dr. Carpenter said he should like to say a few words about the 

 arrangement of Professor Abbe. He had paid a great deal of atten- 

 tion to the subject of binocular vision, and might say that he had 

 been at the birth of the binociilar Microscope. As regarded the one 

 now exhibited, it seemed to him to have been overlooked that in order 

 to get a true stereoscopic projection the rays from one side of the 

 objective must cross completely over to the opposite side of the 

 instrument. This was done in Nachet's and in Wenham's, and with 

 either of these it was impossible to see an object in any other way 

 than stereoscopically. To produce this effect it was necessary that 

 the lateral inversion should be antagonized by the reflecting power of 

 the prism — they must have the reflected ray crossing the other 

 entirely, otherwise they could not have any true stereoscopic efi'ect. 



Another observation which he had to make was that the arrange- 

 ment now described resembled Mr. Wenham's arrangement for a non- 

 stereoscopic binocular. In this form Mr. Wenham made his two 

 prisms in the same way, and except that they were in contact the 

 thing was the same ; it was devised for the purpose of diminishing 

 the fatigue of working with one eye so as to give a more comfortable 

 view of an object in case of prolonged observation, and this was 

 described and figured in the ' Transactiotis ' of the Society for 1866 

 (N. S. xiv. pp. 1U3-6, 3 figs.). In the true stereoscopic binocular the 

 pencil of light was split into two halves, and in Mr. Wenham's standard 

 form one lateral half went into the principal body and the other was 

 reflected obliquely into the secondary body. But this new form did 



