436 



Notes. 



condenser ; it however did not become popular here, as the achro- 

 matised condenser was preferred. 



The following (see next page) are in the possession of the author. 

 The numerical apertures and the optical indices are from actual mea- 

 surement. 



^ It is very difficult at this date to ascertain who was the inventor 

 of the various improvements in objectives ; nothing was published 

 about any improvement at the time of its introduction, and much 

 secrecy was observed. I should be disposed to regard Boss's 1832 



