7O THE MICROSCOPICAL NEWS, 
bring about the proper correction for use with water, glycerine, or 
homogeneous fluid, or for a considerable length of draw tube. 
The magnifying power—measured at ten inches from the front 
lens—is, at the open point, 63, at the closed point 70 diameters. 
The angular aperture is given as 130° in balsam, and is constant 
throughout the entire range of the collar—if the same fluid be 
used. The residual colour is somewhat greater than is usually 
seen in Spencer’s objective ; but still it is well corrected, and the 
field is flat. 
This objective is remarkably sensitive as regards spherical 
aberration, and a slight change in length of body, or so called 
homogeneous fluid, makes itself known by a disturbance of the 
spherical correction. 
The special quality desired —that of resolution —is not dis- 
appointing. The diatoms of Moller’s balsam plate are easily 
resolved—No. 16 in dots by central light, and No. 18 in dots by 
oblique light—lamplight. 
Accepting the orthodox view, it would seem unreasonable to 
expect such an objective to do well on histological work, but, on 
the contrary, it works beautifully. The circulation of blood in a 
frog’s foot is beautifully shown with this glass—using it, of course, 
as a water immersion, without covering glass, and with powers as 
high as 1,000 diameters. The white corpuscles can be seen 
better than with any narrow angled glass with which I am 
acquainted. I regard a frog’s foot as a very good histological 
test. The circulation of blood and contraction of the muscles in 
the leg of Ranatra fusca are also beautifully shown by this one- 
sixth. 
It seems to me that it is a great mistake to put a wide-angled 
objective—even though it be homogeneous immersion—in a non- 
adjustable mount, for it so frequently happens that the length of 
body or density of the immersion fluid varies from that for which 
the objective was originally corrected, and in such cases the best 
performance of the objective is lost. Not only should it be 
adjustable, but it should have sufficient range of adjustment to 
correct for water, as water is far better suited to work over tem- 
porary slides than either glycerine or homogeneous fluid.— American 
Monthly Microscopical Journal. 
