154 CORRESPONDENCE. 



immersion aperture claimed by Mr. Tolles is utterly impossible in 

 this case. 



Many regret the reappearance of this miserable controversy con- 

 cerning Mr. Tolles' ^tb, occupying as it has done over two years in 

 time ; but, like an ill-bealed sore, it breaks out again. My experi- 

 ments and discoveries relating to the microscope have been made for 

 the love of the science, they have been fully explained and freely 

 given at my own cost without a thought of pecuniary interest. Can 

 some of my opponents declare the same ? Confessedly having a 

 purjjose, they never tire of bringing the name prominently forward. 

 I cannot blame the motive, although it is a quaint method of adver- 

 tising.* But let me express my belief that Col. Woodward and 

 Professor Keith are far above this, and I do not doubt for a moment 

 that they have discussed the question wdth strict integrity in accord- 

 ance with the purport of their ideas concerning the optics of the 

 microscope, and if I have not shown that deference for their opinions 

 that some would fain exact,'!' it is not for want of respect ; but having 

 carried on experimental and practical inquiries on these subjects more 

 or less for twenty-five years, I consider that tbe experience that I 

 have gained entitles me to an opinion and some authority in these 

 questions. 



And what does all this wearisome controversy, with its bickerings 

 and misquotations, tend to ? Merely a desire to show that I deny that 

 a greater angle than 82° can be obtained with the immersion lens on 

 a balsam-mounted object. I do not make any such contradiction ; 

 my assertion is, that not only Mr. Tolles' object-glasses, but all others 

 that I have yet seen, do not give near an angle of 82^ in balsam. 



I myself claim to be the first that suggested and made a practical 

 combination or doublet front that would give undiminished angles 

 thus mounted. The principle was described by me in the ' Quarterly 

 Journal of Microscopical Science,' No. xii., July, 1855. Had this 

 been suggested by anyone else, it would have been eagerly quoted 

 against me in controversy, to show that angles beyond 82° could be 

 got in balsam. This was a special adaptation for that very purpose ; 

 I have referred to it several times in evidence of my position, and 

 called Mr. Mayall's attention to it jiarticularly, but it is simply 

 ignored. I here re^^roduce the diagram. The lens (nearly a hemi- 

 sphere) is connected by Canada balsam to the covering glass of a 

 balsam-moixnted object situated in the centre at a. " It will be seen 



* "His (Mr. Wenhani's) recent papers have drawn the attention of niicro- 

 Bcopisfs throughout Europe and America to the work of a brother optician, more 

 effectually than anything else could have done, and have exhibited more con- 

 clusively the difficulties overcome, and illustrated more strongly the skill mani- 

 fested in so overcoming them, than anytliing the otlier would have ventured to 

 eay for himself."— Charles Stodder, 'M. M.J.,' Feb. 1, 1874. 



" And now feel under great obligations to him for originating the discussion 

 or controversy, which lias done so much to bring into notice, both in America 

 and Europe, the merits of American workmanship." — Ibid., Dec. 1, 1875. 



t ''While the other (Mr. Tolles), not content with liaving tlie splendid testi- 

 moni/ of Dr. Woodward and Profe.ssor Keith in his favour, must needs venture to 

 speak in his own behalf, with almost disastrous eflfect to his own lucidity." — 

 J. Mayall, ' M. M. J.,' Aug. 1875, page 93. 



