PROCEEDINGS OF THE SOCIETY. 375 



Jung's Objective-holder, with an ingenious arrangement for re- 

 leasing the objective (ante, p. 132). 



AN estien's Lens-holder, with universal nut for loosening all the 

 parts by one turn of the screw (Vol. V. (1885) p. 316). 



Prof. S. Exner's miero-rcfractometer was exhibited and described 

 by Mr. Crisp. The designer claimed that by a movable diaphragm 

 over the eye-piece he was able to detect differences in the structure 

 of the different parts of blood-corpuscles, insects' eyes, &c. (supra, 

 p. 328). 



Mr. E. M. Nelson described a Microscope (exhibited by Mr. 

 Crisp) fitted by Messrs. Swift with the new form of fine adjustment 

 invented by the Eev. J. Campbell, a clergyman in Shetland, which 

 consisted in cutting two difierent threads on the screw — 32 and 30 

 respectively — giving a rate of motion corresponding to the difference 

 between the two {supra, p. 324). 



Mr. J. Mayall, jun., understood that Mr. Swift thought the 

 arrangement would hardly be likely to serve its purpose for students' 

 Microscopes, for which it had been more especially recommended, as 

 it could not be produced cheaply.* 



Mr. J. Mayall, jun , described a new form of fine adjustment 

 (exhibited by Mr. Crisp) applied to the ordinary Jackson form. It 

 had been designed by Messrs. Anderson and Sons to give two difierent 

 speeds by means of threads having a pitch of 40 and 100 threads to 

 the inch (supra, p. 325). 



He also exhibited a Huyghenian eye-piece which had been made 

 by Mr. Hilger, with lenses of rock crystal. It had been expected 

 that it would give good results; but having tried it carefully, he 

 could hardly tell the diff'erence between this and others of similar 

 power with glass lenses by Messrs. Powell and Lealand. 



Mr. Crisp reported the discovery by Prof. Abbe and Dr. Schott 

 (after several years of work) of a new optical glass, by which the 

 secondary spectrum in objectives was eliminated. Two objectives 

 made from it were exhibited (by Mr. Stephenson and Mr. Crisp) with 

 the special eye-pieces which were designed for use with them (supra, 

 p. 316). 



Mr. Stephenson, in reply to the President, said that to enable the 

 Fellows to judge of the excellence of the .new objectives — one of 

 which had been very handsomely presented to him by Mr. Zeiss — he 

 had brought it to that meeting. He had placed under the instrument 

 a slide of Amphipleura pellucicla in phosphorus, and there could be no 

 question, in his opinion, of the fineness of the definition, w^hile the 

 colourless image and great flatness of field could not fail to strike the 

 observer. The President, in his last address, spoke of the great 

 advantage to practical observation which he had experienced in the 

 increased aperture of modern objectives, and, just in the same way, 



* Mr. Baker informs lis that he finds the arrangement works admirably, and 

 that he applies it to all his Students' Microscopes. 



