162 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
MICROSCOPY. 
a. Instruments, Accessories, &c.* 
Cl) Stands. 
' Stands and various Equipments .f — Attention may be called to an 
editorial article in which recommendable stands are described from the 
catalogues of Zeiss, Schieck, Leitz, and others. General remarks are 
made concerning apertures, eye-pieces, magnifying power, apochromatic 
lenses, focusing arrangements, and the methods of using Abbe’s aperto- 
meter and test-plate. 
(2) Eye-pieces and Objectives. 
Apertures of Objectives.^ — Mr. R. B. L. Rawlings describes a 
simple method for roughly comparing the apertures of objectives, to be 
used when the Abbe apertometer is not available. As in the Abbe 
instrument, § a 3 in. auxiliary objective is attached to the under part 
of the draw-tube ; but in place of the bevelled semicircular glass 
plate, a sub-stage condenser and an iris diaphragm are used. The 
objective to be examined is first focused on the upper surface of the 
condenser, and then, without disturbing this adjustment, the auxiliary 
objective is screwed to the draw-tube, which is slid into such a posi- 
tion that the diaphragm is clearly seen ; when the margin of the dia- 
phragm is brought to the edge of the field of view, the diameter of the 
opening is in direct ratio to the aperture of the objective. Examining 
another objective in the same way, the apertures of the two are propor- 
tional to the diameters of the diaphragm openings in the two cases. It 
is suggested that a direct reading of the aperture could be made by 
combining the iris diaphragm with a graduated arc and index pointer ; 
this would give a measure of the diameter of the opening, and so a 
measure of the aperture of the objective. 
' £3) Illuminating and other Apparatus. 
Monochromatic Light Apparatus.il — Mr. A. E. Tutton describes an 
instrument of precision for producing monochromatic light of any de- 
sired wave-length, and explains its use in the investigation of the 
optical properties of crystals. It consists essentially of a spectroscope, 
with one large 60° prism, in which the eye-piece of the telescope is 
replaced by a fixed slit. Light of different colours is caused to pass 
through this slit by rotating the dispersing apparatus, the position of 
which can be read off on the graduated circle, and this, after the instru- 
ment has been empirically graduated, will give an indication of the 
* 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 Zeitschr. f. ang. Mikr., ii. (1897) pp. 321-35 (2 figs.). 
% Amer. Mon. Micr. Jourm, xviii. (1897) pp. 3-6 ; and English Mechanic, lxv. 
(1897) pp. 57-8. § This Journal, 1878, p. 19; 1880, p. 20; 1896, p. 247. 
|| Phil. Trans., clxxxv. (1894) A, pp. 913-41 ; and Zeits. f. Krystal]., xxiv. (1895) 
pp. 455-74 (7 figs.). 
