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V. — Report on Lenses and other Optical Apparatus of 

 the Lister Legacy. 



By Edmund J. Spitta, L.R.C.P. F.K.A.S. 



{Bead February 19, 1913.) 



The Lister legacy was presented to the Royal Microscopical 

 Society by Sir Kickman Godlee, President of the Royal College of 

 Surgeons, on behalf of the Executors of the late Lord Lister, O.M., 

 in the summer of 1912, and comprised a bust, mounted on pedestal, 

 of Joseph Jackson Lister, F.R.S. (born 1786 ; died 1869), the father 

 of the testator, and one of the Founders of the Royal Microscopical 

 Society ; together with numerous manuscripts (unpublished papers 

 and memoranda of observations and experiments) ; some experi- 

 mental lenses, test-objects, micrometers, etc., belonging to or manu- 

 factured by Lister. Mr. Conrady's notes upon the unpublished 

 papers, together with a complete paper l^y Lister, " Od the Limit 

 of Defining-power," appeared in this Journal for February 1913. 



The packets, cases, and boxes comprising this portion of the 

 bequest contained : — 



1. Many brass mounts, several single and compound lenses, and 

 a few complete and mounted objectives for the Microscope. 



2. Various test-objects — chiefly for the telescope — micro- 

 meters, etc. 



The accumulation of dust inside the various lens-combinations 

 was such as to necessitate the taking apart of each combination 

 (but very few were cemented), the cleaning of each lens, and the 

 re-assembling and adjusting of the components, so as to furnish the 

 best possible results. When this had been successfully accom- 

 plished Mr. Conrady went over the lenses with me, and we finally 

 agreed as to their performances. 



From a careful consideration of the material at our disposal, it 

 is evident that Lister's practical work was at first directed to the 

 making of doublets, in doing which he experimented with all 

 kinds of glasses, both English and foreign. He then became more 

 ambitious, and launched out into the computation of combinations, 

 his early efforts being confined to low powers, such as l^-in., but 

 later on to others of much shorter focal length. This I believe 

 to be the case, because we actually possess one hemispherical un- 

 achromatic front which could not be for an objective of less than 

 J-in., possibly J in., or even yV"^^- f^^^al length. 



This collection of objectives, etc., must be regarded as of con- 



