248 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
the field of view by adjusting the position of the slit by means of the 
screw s r The screw s 2 serves to regulate the width of the slit. 
The apparatus is connected with the Abbe illuminator by a centering 
collar. 
Microscope-Stage with Iris-Diaphragm.* — Dr. W. Behrens de- 
scribes the stage with iris-diaphragm made by Meyer & Co., to facili- 
tate the change from condenser-illumination to diaphragm-illumination. 
The aperture f>f the stage is larger than usual, having a diameter of 
23 mm. The short cylinder with the iris-diaphragm is fixed by a round 
brass plate, screwed into the under part of the stage. On the right this 
plate is cut away to make room for the handle of the iris-diaphragm, 
which is so long as to project beyond the side of the round stage. 
Beneath the diaphragm is the condenser, which on racking down can be 
turned to one side. 
(4) Photomicrography. 
New Method of Illumination for Photomicrography, f — Mr. J. 
Hunter draws attention to the fact that a paper under the above title 
was read by him before the Scottish Microscopical Society in 1891. 
The method there advocated, and more fully described in the present 
paper, has many points in common with the method described by 
Dr. Kohler in a paper in the Zeitschr. f. wiss. Mikr. in 1893, an 
abstract of which appeared in this Journal, 1894, p. 261. The optical 
conditions in the two methods are essentially identical; in both an 
evenly illuminated disc, instead of an image of the source of light, is 
thrown upon the slide by a condenser. The author’s scheme, however, 
differs from that of Dr. Kohler in the detail that in it, instead of the 
ordinary plano-convex lens 0,J he uses a triple form of condenser con- 
sisting of a flint-glass shell, a correcting lens of crown glass, and the 
interspace filled with pure water. This producess a very perfect form 
of aplanatic condenser possessing many capabilities. Minor differences 
are that the diaphragms at s b and J are dispensed with, and that an 
equi-convex lens is used instead of the plano-convex lens at S Z. In 
the course of a detailed account of his method, the author strongly 
advocates the use of corrected condensers, and states that superior 
results should be expected from his apparatus owing to the use of the 
aplanatic condenser instead of the ordinary plano-convex lens in Dr. 
Kohler’s arrangement. 
The merits of the new system are : — (1) . The whole field is 
uniformly luminous. (2) The illuminating rays are parallel. (3) The 
extent of luminous area, as well as angle of aperture, can be easily 
altered to suit the objective. (4) The heat of the flame is rendered 
harmless by position. (5) The water compartment of the condenser 
obviates the use of an alum-cell. (6) Monochromatic light can be 
readily obtained by dropping the required tint into the water of the 
lens. {7') In the same way the lens may act as a colour-screen. 
(8) The correction of the lens is very perfect. (9) Edge interference 
* Zeitschr. f. wiss. Mikr., xif (1896) pp. 292-5. 
f Proc. Scottish Micr. Soc., 1894-5, pp. 229-56. 
X See this Journal, 1894, p. 261, fig. 23. 
