JOURNAL 
OF THE 
ROYAL MICROSCOPICAL SOCIETY. 
ArRIL 1892. 
TRANSACTIONS OF THE SOCIETY. 
I II . — The Resolution of Arnphipleura pellucida. 
By J. W. GlFFOIiD. 
( Raid 18</( Xoveniber, 1891.) 
Pi. ate III. 
In September last, Mr. C. Lees Curties was kind enough to show me 
a prism arrangement devised by Mr. Nelson for the production of 
monochromatic light in a form adapted for use with high power 
Microscope objectives. He drew my attention to the advantages 
attendant on its use, and showed me a frustule of Surirella gemma , 
clearly resolved by a Zeiss apochromatic 6 mm. In the course of 
conversation I asked if it were a fact, that, as reported, A. pellucida 
had been resolved into distinct dots by the new Zeiss apochromatic 
2 - 5 mm. of 1 ’6 N.A. On this he expressed a doubt,* but remarked 
that A. Lindheimeri was without difficulty so resolvable. 
I then thought the matter out and determined to examine a 
frustule of A. pellucida with sodium flame illumination, as being the 
most convenient and effective form of monochromatic light I could 
think of at the time. I was much pleased to find, even at the first 
attempt, that A. pellucida unmistakably showed dots, which became 
much more marked as the frustule was shifted to the side of the field of 
view. 
At this point I communicated with Mr. Curties, who advised me 
to photograph what I had seen. And now the question arose as to 
the possibility of producing such photographs by the light of the sodium 
flame, and Mr. Curties very materially helped me by suggesting bathed 
plates, treated with an erythrosine bath. 
EXPLANATION OF PLATE III. 
Fig. 1 x 1300; taken with Powell & Lealand’s O.I. 1/12 in. N.A. L43. 
” 3 x 2080 } *' a ' ien w Rh Powell & Lealand’s O.I. 1/20 in. N.A. 1*5. 
* Dr. Van Heurok has published photomicrographs of this diatom with tlie 
leading clearly shown by means of the 2 - 5 obj. N.A. 1 ' 00. These were produced in 
this Journal, and a separate plate with the same result is given in Dr. Dallin°-er’s 
(7th) edition of ‘The Revelations of the Microscope,’ 1801. — [Ed. J.R.M.S.] 
1892. o 
