79 



What was the Amician Test ? 



By George C. Karop, F.R.M.S. 



{Read March lUh, 1895.) 



In reading the earlier papers on microscopy, that is to say in 

 the modern sense of the word, when successive improvements 

 were being made in the construction of objectives by enlargement 

 of their aperture and hence in their defining power ; at a time 

 when the dilettanti were vying with one another in the resolution 

 of diatoms by the aid of condensers, prisms, oblique illuminators 

 and what not, one frequently comes across the phrase " Amician 

 test." It is used so definitely as a touchstone of excellence, either 

 in object glass or manipulative skill, that one must assume the 

 exact nature of this " test " was the common knowledge of every 

 microscopist of the period, but I must confess, after some amount 

 of search and personal inquiry from those most likely to remember, 

 it still remains to me a matter of uncertainty. I do not wish it 

 to be understood for a moment that I have made an exhaustive, 

 or even an extended, investigation on the subject ; I have not been 

 able to find any statement by Amici himself or by anyone whose 

 authority might be accepted as final, but I have looked through 

 the few text-books of the period and papers on manipulation in 

 various transactions, etc. It is simply for my own instruction 

 and with a view of eliciting information from others that I have 

 ventured to put this interesting question before you to-night. 



The first, or most probable, solution that presents itself is that 

 Amici made use of several tests of increasing difficulty as he 

 improved the construction and resolution of his lenses. Indeed 

 it is certain, in his earlier efforts with specula and objectives, that 

 he employed scales of various LepiJoptera, Podurae and so forth, 

 which were the first test objects whatsoever for comparing the 

 quality of lenses. The use of these scales for the purpose of 

 testing the aperture of objectives was discovered by Dr. C. R. 

 Goring. 



