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II. — The l/jipuhlished Papers of J. J. Lister. 

 By a. E. Conk ad y. 



[A considerable number of notes and manuscripts on optical subjects 

 bj J. J. Lister — best known, hitherto, for his discovery of the two 

 aplanatic foci of ordinary achromatic combinations and the application of 

 that discovery to the construction of the achromatic doublet — were left 

 to the R. ^I. S. by his son, the celebrated surgeon Lord Lister. 



It is evident from many of the papers, that J. J. Lister himself was 

 proud of his first achievement just mentioned, and it would almost 

 seem as if he had felt as if he were not receiving sufficient credit for his 

 share in the improvement of the achromatic Microscope : that is the 

 impression left on the present writer, by the following autobiographical 

 note found among the papers, the heading being in a different hand, 

 presumably Lord Lister's :] 



Found in paper marked 1837, etc., Memoranda for and of 



A. Boss. 



" I had been from early life fond of the Compound Microscope, 

 but had not thought of improving its object-glass till about the 

 year 1824, when I saw at Mr. Tulley's, an achromatic combination, 

 made by him at Dr. Ewing's suggestion, of tw^o convex lenses of 

 plate-glass with a concave of flint-glass between them, on the plan 

 of the telescope objective. They were very thick and clumsy. I 

 showed him this by a tracing with a camera-lucida, which I had 

 attached to my Microscope, and the suggestions resulted in 

 " Tulley's j^^", which because the microscopic object-glass of the 

 time. But the subject continued to engage my thoughts, and 

 resulted in the paper, " On the Improvement of Compound Micro- 

 scopes," read before the Royal Society, January 14, 1830^ (Phil. 

 Trans., xxi. J.L., 1870), announcing the discovery of the existence 

 of two aplonatic foci in a double achromatic object-glass. 



" This has formed a basis for subsequent important improve- 

 ments, the object of which has always been to obtain sharpness 

 and achromatism over the field in the picture from a larger and 

 larger pencil, this being an essential to obtaining higher and higher 

 defining power. After succeeding fairly in a trial combination, 

 with this view I left the subject for a while, hoping it would be 

 pursued by opticians ; but the glasses produced by the makers con- 

 tinued to be on the first simple construction of two or three plano- 

 convex compound lenses till the beginning of 1837. At that time 

 I called on Andrew^ Ross regarding some object-glasses he had 

 made to a Microscope for :\Ir. Owen, when he told me he had been 



