264 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
In the Abbe drawing apparatus two smoked glasses are provided for 
reducing the light of the plane of the drawing, which is usually the more 
intense. In order to allow of finer gradations in the reduction of the 
intensity of the light of both image and drawing plane, the author has 
modified the Abbe apparatus in the following way : — For the two smoked 
glasses for diminishing the intensity of the light of the drawing plane 
are substituted two circular diaphragms, each of which contains four 
smoked glasses of different degrees of darkness. These are hinged on 
an arm so that each alone or both together can be inserted between the 
prism and mirror, or rotated to one side at will. The central position 
for each glass between the jmsm and mirror is marked by a catch. 
For reducing the intensity of the image, a third horizontal rotating 
diaphragm is placed below the prism ; it is of the same size as the other 
two, and, like them, possesses four apertures, three of which contain 
smoked glasses, while the fourth gives free passage to the rays out of the 
Microscope. The three diaphragms together allow of exactly 100 possible 
combinations. 
Winkers new Drawing Apparatus.* — Dr. H. Henking describes 
the new drawing apparatus of Winkel. In principle it is not new, 
since it closely resembles the apparatus described by G. Kohl, as well 
as that recently brought out by the firm of Zeiss. In all three the 
image is projected by a mirror inclined at 45° upon the horizontal table 
on which the Microscope stands. The union of the plane of the object 
and plane of the image on the retina is effected by Winkel by means of 
a prism, w'hich carries in the centre of the hypothenuse face a small 
glass cylinder. This cylinder is cut obliquely where it is attached to 
the prism, so that it stands vertically and transmits to the eye the rays 
coming from the Microscope. The hypothenuse face of the prism is 
silvered. For diminishing the intensity of the light he inserts between 
prism and mirror a rotating diaphragm having five apertures, three of 
which contain smoked glasses, while the fourth carries a bluish glass, 
and the fifth has none. The correct position for each glass between prism 
and mirror is marked by a catch. The arm which carries the mirror is 
in two parts, so that the distance of the mirror can be varied by one part 
sliding in the other. Prism, rotating diaphragm, and mirror are carried 
on a common arm, which is not in rigid connection with the spring socket 
by which the apparatus is attached to the Microscope, but is movable 
about a horizontal pin, so that the arm with prism, &c., can be rotated 
to one side. Lastly, a special clamping-screw permits of the adjustment 
of the height of the pin, and with it the prism, &c., so as to suit different 
eye-pieces. 
The Grapho-Prism and its Use.f — Dr. F. Gaertner writes : — “To a 
practical microscopist who is not also a skilled artist, perhaps nothing is 
more important among microscopical accessories than the camera lucida, 
or grapho-prism. This prism is an instrument for sketching objects with 
ttie point of a pencil upon a piece of paper laid beside the Microscope. 
By its use a high degree of accuracy may be attained. Perhaps the 
simplest and most successful drawing prism is that of Zeiss, which is 
* Zeitschr. f. AYiss. Mikr., viii. (1891) pp. 295-7. 
t Auier. Mon. Micr. Journ., xii. (It91) pp. 265-7. 
