NATURAL HISTORY MISCELLANY. 797 
a very curious department of microscopical study, the details of 
which are published in the ‘t Monthly Microscopical Journal.” He 
combines the spectroscope with the polarizing microscope, in or- 
der to analyze the colors given by double refracting crystals 
when viewed by polarized light. In his arrangement, the light 
from the mirror passes first through an adjustable slit below the 
isubstage, then through a Nicol’s prism and the achromatic con- 
denser, and forms an image of the slit on the double refracting 
crystal on the stage. The dispersion prisms are placed above the 
objective, and the spectrum is viewed with the eye-piece and ana- 
lyzing prism. Those who prefer to use the spectroscopic eye- 
piece, as most do in this country, would dispense with the slit 
below the substage, and place the analyzing prism over the objec- 
tive. 
A Hien One-rivra. — Assist. Surg. J. J. Woodward, U. S. A., 
resolves Amphipleura pellucida with a Tolles immersion one-fifth. 
This is a high one-fifth, but much less than a one-sixth in pow- 
er. Angular aperture 110° to 170° according to adjustment. As 
these lines count ninety-six thousand to the inch, Dr. Woodward 
expected that it might resolve the sixteenth band of Nobert’s 
plate. He only succeeded, however, in getting through the fif- 
teenth band. This result corresponds with his judgment, based 
upon other observations, that Nobert’s lines are more difficult of | 
resolution than lines of equal fineness on the natural objects usu- 
- ally studied in comparison with them. 
FRESH-WATER ALGÆ.— Dr. T. C. Hilgard’s paper on this subject, 
read before the Microscopical Section of the American Association 
at the Indianapolis meeting, was inadvertently omitted from the 
list of papers published in the Association Number of the Natu- 
RALIST. 
PHOTOGRAPHING HISTOLOGICAL Prerarations.— Dr. Woodward 
describes in the ‘ American Journal of Science and Arts” for 
October certain improved methods of using the light of the sun 
for photographing the soft tissues. 
Noserr’s Lixes.—President Barnard judges that it is not neces- 
sary to count the whole of one of Nobert’s bands in order to re- 
solve it unmistakably, but only to count a measured portion of a 
band. 
