JOURNAL 
OF THE 
ROYAL MICROSCOPICAL SOCIETY. 
AUGUST 1898. 
TRANSACTIONS OF THE SOCIETY. 
X . — On a New Apoehromatic Objective constructed without the 
TJse of Fluorite . 
By Philip E. Bertrand Jourdain, F.R.M.S. 
(Head 18 th May , 1898.) 
Semi-apochrowatic lenses made of hard glass can be produced, as 
Mr. E. M. Nelson * has pointed out when speaking of some by Leitz, 
Fig. 72. 
Apoehromatic objective ; 
2/3 in. ( x 2). 
Fig. 73. 
Projection ocular (8) 
( X 2). 
which are very highly corrected as to 
colour ; in one case such an objective was 
hardly distinguishable from the earlier 
apochromats of Zeiss. Apoehromatic 
lenses can also be constructed if the soft 
glasses of Schott & Co. are used, but their 
permanency is doubtful. 
Prof. Charles S. Hastings recently, 
however, computed an apoehromatic ob- 
jective without fluorite, which is stated to 
be of permanent materials. I am able, 
through the courtesy of the makers, 
Messrs. Bausch and Lomb, to give a 
sectional drawing of an objective and 
projection ocular ; but no information 
1898 
* Journ. Roy. Micr. Soc., 1897, p. 349. 
