30 _ THE Microscope. 
5. What is the use of the adjustment-collar, and how is it used? 
I have a Tolles 1-10, Wales 1-15, ete. AB: 
6. What is the best way to remount delicate specimens (mounted 
five years | in which the glycerine has partly dried up and the cement 
‘has mixed in slightly ? ey 
7. Where can I get plants analyzed, to get their proper names ? 
I have some plants sectionized, but cannot identify them in Gray’s 
Botany. One is a vine, has red berries, more like small grapes, but 
in umbells, the leaves pinnately parted. 
J. D. Buck. 
7. (Ans.)—Perhaps the editors of the Bulletin of the Torrey 
Botanical Club, Columbia College, New York, or the Botanical 
Gazette, Crawfordsville, Ind. 
8. What is the best apparatus by which to get a good back- 
ground illumination at night? Ihave seen some apparatus used 
which gave an excellent bluish daylight effect, but don’t know what 
it was. diss 
Bureau or MergoroLocy oF THE NORTHWESTERN UNIVERSITY, 
Cuicaco, December 31, 1888. 
EDItorSs OF THE Microscope: 
T have recently had the opportunity of examining several of 
Zeiss’s apochromatic objectives in competition with the recent work 
of Mr. Herbert R. Spencer, and of the Bausch & Lomb Optical Co. 
Unfortunately, Messrs. Bausch & Lomb had no homogeneous immer- 
sion objective of recent manufacture on hand; but the comparison of 
the first class + with a Zeiss apochromatic of the same power, to my 
mind, demonstrated that the Bausch & Lomb }+ was quite equal to 
the Zeiss, if not superior to it. 
‘The comparison of the Zeiss ;'; apochromatic, N. A., 130, and 
of a 1 and 1 apochromatic, with Mr. Spencer’s latest work, resulted 
unfavorably to the Zeiss. In my opinion, the Spencer objectives 
were decidedly superior to the Zeiss, and this was especially the case 
in the comparison of the homogeneous immersion objectives of these 
makers. 
I think the durability of the flint glass used by Mr. Zeiss in his 
apochromatics may fairly be questioned. In three Zeiss apochro- 
matics, which I have recently had the opportunity of examining, the 
lenses made of this glass showed clear evidence either of deteriora- 
tion or of having been imperfectly polished when sent out, which 
latter is highly improbable. 
