676 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
times the aplanatic of 14 cm., for 8-25 times that of 7 cm. focal length. 
Many of the Hartnack systems, however, are not inferior to these. For 
magnifications of 20-55 Hartnack’s embryograph was found to be the 
best. For medium magnifications of 50-300 times the Seibert systems 
of 1, 1/2 and 1/4 in. were used, and for magnifications above 300, the 
Zeiss projection eye-piece with the dry apochromatics of 8 and 4 mm. 
focal length. 
With high magnifications a difficulty was experienced with respect 
to the clamping of the preparation on the object-stage. Owing to the 
unequal pressure of the two clamps the preparation was not at right 
angles to the axis of the Microscope. This difficulty was removed by 
attaching to the stage a plate which could be levelled by screws. The 
clamps, three in number, were screwed to this plate, and their pressure 
on the object-slide was thus regulated. 
The course of the operations for low or medium magnifications is 
as follows. After fixing the objective and closing the current in the 
electric lamp, the magnification is determined. For this purpose a 
small glass scale divided in half or tenth millimetres is adjusted on 
the stage of slide 2, and the frame in the dark room is moved until 
the desired magnification is obtained. The proper illumination is then 
considered. The first illuminating lens (20 cm. focal length) in the 
lantern is once for all adjusted so that the rays fall approximately 
parallel and fill the aperture of the second lens on slide 1. 
This slide is then displaced until the point of the pencil of rays 
falls in the plane of the diaphragm of the objective. 
The preparation is now placed on the stage, and the fine-adjust- 
ment is made from the dark room. The current is then broken and 
the two shutters and the front door of the dark room are closed. 
The plate-frames are then laid down and the sensitive paper in- 
serted between them. The current is once more closed and the light 
regulated by examination of the white paper in front of the shutter. 
To ascertain whether the image falls properly on the sensitive paper 
the red glass screen is placed before the illuminating lens of slide 1, 
and the shutter is opened, while the object- stage is adjusted. The 
shutter is then closed again, the red glass removed, and the light again 
adjusted. Exposure is then effected by opening the shutter. 
To adjust the apparatus for use with the Microscope-stand, the 
objective- holder is removed and space cleared for the stand. The 
Fritsch’s wheel on the slide is then connected by an intermediate piece 
with the guide in the dark room, and the diaphragm-holder of slide 3 
is adjusted. The Microscope is now screwed upon the slide and 
directed horizontally. The Fritsch’s wheel is raised until it engages 
in the micrometer screw of the Microscope. To insure the proper 
centering of the light the aperture of the iris-diaphragm is made very 
small, and the illuminating lens and carbons are moved until the point 
of the pencil of rays falls just in this aperture. For the later orienta- 
tion on the direction of the pencil of rays a second diaphragm in the 
diaphragm holder is used. The circle of light is made concentric with 
the aperture of the diaphragm. 
After the centering of the light, the iris diaphragm is opened, and 
by means of the large illuminating lens and Abbe condenser the proper 
