728 PROCEEDINGS OF THE SOCIETY. 



Mr. C. L. Curties exhibited two new designs of electric lamps for 

 Microscope use, fitted with ground-glass or blue-glass fronts, and 

 mounted so as to be used at any height or angle required. Those 

 exhibited were made for 100 and 200 volts respectively. 



Dr. Hebb said he had been using one of these lamps at the West- 

 minster Hospital for some weeks, and found that it worked very satis- 

 factorily and gave a very powerful light. 



Mr. Hugh C. Ross exhibited and described a small electric warm stage, 

 formed by a coil of fine wire pressed into an ebonite plate and covered 

 with a piece of mica. It could be slipped on or off the ordinary slide 

 in an instant ; it could be used with the highest powers of the Micro- 

 scope ; it would work on a mechanical stage, and required no attention 

 when in use, maintaining a constant temperature for any length of 

 time. The one exhibited was regulated to give a temperature of 37° C, 

 and a small thermometer attached to the slide showed that this tem- 

 perature did not vary during the evening. He invited the Fellows 

 present to inspect the stage, and to make any suggestions for its im- 

 provement which occurred to them. 



On the motion of the Chairman, a vote of thanks to Mr. Ross for 

 his exhibit and description was unanimously carried. 



Mr. A. E. Conrady gave a lengthy resume of the contents of his 

 paper entitled " Theories of Microscopical Vision : a Vindication of the 

 Abbe Theory," illustrating his remarks by lantern slides and by mathe- 

 matical formulas worked out upon the board. 



Dr. Johnstone Stoney, after referring to the lateness of the hour, 

 which prevented his venturing to criticise Mr. Conrady's suggestive 

 paper, requested permission to avail himself of this, the first opportunity 

 open to him, to call attention to a passage in one of Sir George Stokes's 

 earlier papers, of which he had only lately become aware. 



The Abbe theory, as investigated by its author, relies upon experi- 

 mental evidence ; and when Dr. Stoney, some eleven years ago, made a 

 special study of Prof. Abbe's important explanation of how microscopical 

 images are formed, the inductive proof adduced by Abbe did not seem 

 to him a satisfactory basis on which to rest a theorem of the kind, 

 since, if accurately correct and susceptible of being generalised, it ought 

 to follow deductively, as a necessary consequence of the laws under which 

 the electromagnet waves which constitute light are propagated in uniform 

 media. On a further study of the subject, he found that it is possible to 

 obtain a complete deductive proof of Abbe's results, and to extend them 

 to all optical images, by resolving the optical disturbance in the medium 

 into components, each of which is an undulation of plane wavelets, 

 and in which each of these wavelets is uniform throughout its extent. 

 Dr. Stoney was then and remained until lately under the impression that 

 he was the first to ascertain that every disturbance within a uniform 

 wave-propagating medium is susceptible of being resolved in this way. 

 But a scientific friend has directed his attention to a passage in one of 



