

Examination of Photographic Lenses at Keiu. 403 



Virchow (R.), For. Mem. R.S. Crania Ethnica Americana. Folio. 

 Berlin 1892. The Author. 



Bronze copy of the Gray Prize Medal of the Marischal College, 

 Aberdeen. P. J. Anderson, Esq. 



"On the Method of Examination of Photographic Lenses afc 

 the Kew Observatory." By LEONARD DARWIN, Major, late 

 Royal Engineers. Communicated by Captain ABNEY, C.B. r 

 F.R.S. Received April 13, Read June 2, 1892. 



The Kew Committee of the Royal Society decided, about a year 

 ago, to undertake the examination of photographic lenses, thus 

 adding one more to the already numerous list of tests and certificates 

 issued by the Kew Observatory. Captain Abney was the member of 

 the Committee who originated the idea, and he was requested to 

 organise the system in detail. This he undertook to do, but unfor- 

 tunately it proved that official duties and his work in connexion with 

 colour vision, &c., made it impossible for him to give the necessary time 

 to the enquiry. In consequence of this, I was asked by the Kew Com- 

 mittee, with the full acquiescence of Captain Abney, to give my 

 assistance in the matter, which I gladly consented to do ; eventually 

 the arrangements devolved almost entirely upon myself, acting in co- 

 operation with Mr. Whipple, the Superintendent of the Observatory , 

 and aided by consultations with Captain Abney ; but I should add 

 that as to the arguments and discussion in this paper I alone am 

 responsible. A very considerable amount of time and energy was 

 expended by Mr. Whipple and myself before the final recommenda- 

 tions could be made, but now, since the whole of the proposals have 

 received the provisional approval of the Kew Committee, it is open to 

 anyone to get a photographic lens examined at Kew on payment of a 

 small fee. 



It is important first to state clearly the general idea which the- 

 Kew Committee had in view when they undertook this new work, 

 for, if the methods adopted are judged from any other standpoint, 

 they will, no doubt, be found open to criticism. The object of the 

 Committee was to organise a system by which any one could obtain, 

 on payment, an impartial and authoritative statement of the quality 

 of a lens to be used for ordinary photographic purposes, and that the 

 fee, which had to cover the cost of the examination, should be 

 moderate. This latter consideration acted as a serious restriction, 

 and it was consequently necessary that all the tests should give 

 results of undoubted practical value to the practical photographer ; 

 the certificate of examination must be recorded in the way most 



