516 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
MICROSCOPY. 
a. Instruments, Accessories, &c.* 
Cl) Stands. 
Baker’s Student’s Microscope. — We give a figure (fig. 53) of the 
Student’s Microscope lately made by Messrs. Baker, to which Mr. E. 
M. Nelson called attention at the 
Ftg. 53. March meeting, j 
Zeiss's Crystallographic and 
Petrographical Microscopes. — 
Dr. S. Czapski describes the 
three latest forms of the Zeiss 
petrographical model. 
The base of the large model 
(fig. 54) is of the usual horse- 
shoe form. The body-tube, &c., 
can be inclined and clamped in 
any position down to the horizon- 
tal. The illuminating apparatus, 
which is movable by rack and 
pinion, consists of the condenser 
and the diaphragm and polarizer 
holder. 
The condenser has a nume- 
rical aperture of 1*4 and is 
movable in a socket, so that it 
can be easily removed and re- 
placed by other illuminating 
arrangements, such as 
(1) The achromatic condenser, 
or the special achromatic illu- 
minating apparatus for photo- 
micrography, by which a sharp 
image of the source of light is pro- 
jected on the plane of the object. 
(2) The Bartnack illumi- 
nating apparatus, for monochro- 
matic light. 
(3) The Engelmann microspectral objective. 
(4) The spectro-polarizer of Rollet. 
The polarizer holder carries the iris-diaphragm next to the con- 
denser, and has the nicol P beneath. It is rotated by rack and pinion R, 
and the positions of 0°, 90°, and 180° are marked by a stop. To convert 
from polarized to ordinary light, the holder is simply pivoted aside (as 
represented in fig. 55). 
* This subdivision contains (1) Stands; (2) Eye-pieces and Objectives; (3) Illu- 
minating and other Apparatus ; (4) Photomicrography ; (5) Microscopical Optics 
and Manipulation ; (6) Miscellaneous. t See ante, p. 298. 
X Zeitschr. f. Instrumentenk., xi. (1891) pp. 94-9 (3 figs.). 
