COERESPONDENCE. 



99 



glasses only. It was restricted to these by its very terms. Is the 

 known superiority of immersion-glasses clue to their greater angle ? 

 This was the question in-oijosed. To this it was answered — the 

 cause is certainly not the greater angle ; for the angle is not greater, 

 but confined necessarily within the self-same • limits. On this point 

 issue was joined ; Mr. Tolles declaring that, whatever theory might 

 say, as a matter of fact his own glasses could have and did have 

 a much wider angle. In token of which he finally selected one of 

 these glasses to be tested, the whole issue being staked on the result. 

 This was the question, the only question, in controversy. There was 

 no misunderstanding about it on either side, for the glass selected and 

 sent was an uhject-glass. It was tested, as we all know; first in 

 England, then " on appeal " in America, with the results which like- 

 wise we now all know. 



In course of the discussion, however, Mr. Tolles did, no doubt, 

 introduce, as a kind of " second string," the possibility of the optical 

 machine referred to having an extra hemisphere, which he afterwards 

 put together. But on this subject there never was for a moment any 

 controversy. When introduced, I at once pointed out that this, 

 though manifestly possible, was nothing to the present question. 

 And Mr. Wenham added, that not only was it not the question, but 

 that the construction, such as it was, was his own, published by him 

 many years ago, and practically carried out for the very purpose of 

 testing the eflect of the increased aperture so obtained ; in testimony 

 of which he reprinted his paper in the January number of this Journal, 

 where it may now be read. Yet, notwithstanding this double pub- 

 lication, by a curious inversion of the fi\cts he has been credited with 

 ignorance of his own invention ; while Mr. Tolles, assuming the merit 

 of the idea to himself, finds his claim allowed, as Cleon, in The 

 Knights, threw out his rival by taking the cake the other man had 

 kneaded, and serving it up as his own : — 



TravovpyoTaToi wws irapa^pa/xwu vcpapiraaas 

 aiirhs Trap46T]K€ Trjv vir i/xov /xe/jLayixevriu. 



The construction produced by Mr. Tolles diifers in no way from the 

 other, except that the extra hemisphere, which was formerly left 

 unattached, he disguises by cementing it to the front of the object-glass. 



When, therefore. Dr. Woodward -ni-ites that Mr. Wenham has 

 " overlooked the possible case," I can only account for the mistake 

 of this most eminent microscopist, by supposing that he has inad- 

 vertently omitted to read the article in the January number. 



Such a structure — should it ever come into common use, which is 

 not likely — will not be an " object-glass " in the ordinary sense of the 

 word. To call it an objective " of four systems " is a misuse of language, 

 because it implies a false idea of its structure. It implies that the 

 four systems are systems in the same sense of the term, which is not 

 true. A one-inch, e.g., has two systems; and in. the very same sense 

 of the word a quarter has three, because the third system while cor- 

 recting the action of the front leaves the conditions of vision exactly 

 the same. And in this way we might have, if necessary, a dozen cor- 

 rective systems behind these. But here the fourth " system " is not a 

 YOL. X. I 



