Optical Curiosities of Literature. 227 



have it in meal and also in malt. Mr. ToUes, however, having taken 

 a good while to think of it, imagined that he could. The front of 

 his object-glass he uses to pass the rays straight on, the refraction 

 being neutralized with fluid. Then, oblivious of having used it up, 

 he all the same expects the benefit of its action the other way, as a 

 refracting surface collecting the pencil for the eye-piece. 



I think that this may fairly pair off with the discovery of the 

 man with the diagram of the great and small mirrors. 



Mr. T.'s ingenious idea was disposed of by Mr. Wenham in a 

 single line, by asking the question, " Do you expect to coUect your 

 whole aperture with the back combinations ? " And after this it 

 might have been supposed that Mr. T., in silence and meditation, 

 had learned at length to avoid the pitfalls of this question. But from 

 an incident which has since occurred I gather, with regret, that he 

 is still in difficulties. A letter addressed by me to Col. Woodward, 

 under the signature " B," concerning the aperture of his i, Mr. 

 Stodder volunteered to answer (Jan., 1872). He replies for the four 

 cases, immersed and dry, uncover'd and cover'd. In three of the 

 cases the figures are no doubt correct ; in the remaining one — 

 the object immersed, uncover'd — prompted by Mr. Tolles he reports 

 the aperture as 140^ ! ! ! Col. Woodward, who also courteously 

 replied, also answers for the four cases ; but, better instructed than 

 his countrymen, on coming to the critical case he leaves out the 

 figure, restricting himself to saying that, after a certain turn of the 

 screw, the glass may now be used for objects immersed uncover'd. 



I pass to notice some other passages remarkable in difi'erent 

 ways, but not for the same kind of reasons as these. I insert them 

 here for convenience only, and in no sense intending to class them 

 with those already given. 



In a paper by the late President, the Eev. J. B. Keade, a 

 sentence occurs which seems difficult to account for. Experiment- 

 ing with his prism, he announces* that when it is turned so as to 

 reflect light to the tube from its upper plane face the beam will be 

 found to be polarized. This he gives as a fact so novel and startling, 

 that he even anticipates it will be received with incredulity — " as a 

 fable." Can it be that he was till then not aware that at a certain 

 angle light is polarized by reflexion ? He was before my time ; 

 but I have always understood that his scientific attainments, more 

 especially in optics, were of a very high order. Yet in this passage 

 he speaks precisely as Mains might have spoken on that evening 

 when, sixty years ago, to his own astonishment he " vanished " the 

 sun's reflexion from the windows of the Luxembourg with his 

 doubly-refracting prism. It may be, however, and I should be glad 

 if it can be shown, that the passage was meant to bear some other 

 meaning, and that the mistake is mine. 



* Vul. ii., p. 83. 



