PROCEEDINGS OF THE SOCIETY. 783 



The thanks of the Meeting were voted to Dr. Horder for his exhibit 

 and explanation. 



Mr. Taverner exhibited upon the screen two photographs of the leg 

 of a water mite which he had taken through the separate tubes of a 

 binocular microscope. He said this experiment proved the images seen 

 by each eye were really dissimilar and capable of producing a true 

 stereoscopic effect ; if they had been alike the apparent solidity of the 

 object as seen through the binocular would be only a mental effect. He 

 found in this way that there was a sufficient difference between the 

 pictures to produce a proper stereoscopic projection. 



The thanks of the Society were voted to Mr. Taverner for his 

 exhibit. 



Prof. J. D. Everett, F.R.S., read a "Note" on Lord Kayleigh's. 

 paper of 1896, reprinted in the Society's Journal for August, pp. 

 447-473. 



There was one part of the paper in question that he had always 

 found specially difficult, namely that in which the transition is made 

 from direct to oblique illumination of a grating under the Microscope. 

 He had recently succeeded in finding a more direct mode of deducing the 

 results there established ; and that mode was set forth in the present com- 

 munication. Lord Eayleigh, to whom he submitted the " Note " several 

 weeks since, had been too much occupied with some special investigations 

 to look thoroughly into the matter, but said that on cursory examination 

 the new method of deduction seemed to be correct. It is intended 

 to supersede the two pages of the original paper which begin with 

 Equation 32 (where' imaginary multipliers make their first appearance) 

 and end with Equation 45. 



He proceeded to explain his proof by diagrams and formulas on the 

 blackboard. 



Dr. Johnstone Stoney prefaced his remarks by observing that he had 

 for several years been engaged in studying optical problems by a new 

 method, and especially microscopical problems of the kind dealt with in 

 Dr. Everett's paper. 



Students of nature did not always sufficiently keep in view the 

 distinction between a hypothesis and a theory. A theory is the best 

 supposition we can form as to what that machinery is which is actually 

 operating in nature ; and accordingly theories are correct or incorrect. 

 Their merit is to be true, irrespective of whether we can make much or 

 little use of them. On the other hand a hypothesis involves the supposi- 

 tion that certain artificial machinery is brought into operation, the study 

 of which we have reason to expect will help us forward in our investiga- 

 tion. The hypothetical machinery may be, either that which we suppose 

 to be operating in nature — in which case the hypothesis is also a theory 

 ■ — or, as more frequently happens, it is simpler machinery which we 

 substitute for some more complex operation going on in nature. It is 

 quite sufficient justification for a hypothesis, that we can make good use 

 of it ; whereas a theory must aim at being true. 



