338 KECORD OF CURRENT RESEARCHES, ETC. 



Eefractive Index of Cover-glass. — In reply to a query by Mr. J. 

 Mayall, jun., as to the nature of the glass used as cover-glass, Dr. 

 Hopkinson, F.R.S., writing on behalf of Messrs. Chance of Birming- 

 ham, states that it is ordinary crown glass having a mean refractive 

 index of 1 ' 5 to 1 • 525, and that they have never used flint glass for 

 the manufacture of microscopical covering glass. This is noted as 

 many microscopists are under the impression that it is flint glass.* 



* See «Mon. Micr. Journ," viii. (1872) p. 271. 



