ULTRAMICROSCOPES 
115 
lyzer is then placed as usual above the ocular of the micro¬ 
scope M. 
To adjust the illuminating beam of light used with the sht 
ultramicroscope shown in the diagram, screw the condenser- 
objective Cs into its holder T. Place the projection lens C2 
at about 10 to 12 centimeters from the end of T, place the 
adjustable slit approximately 12 centimeters from C2, the projec¬ 
tion lens Cl about 12 to 15 centimeters from the slit, the dia¬ 
phragm D 12 to 15 from Ci and the arc lamp so that its carbons 
are about 8 centimeters from D. Turn on the current adjusting 
the rheostat so as to employ a current consumption of approxi¬ 
mately 10 amperes and see that the + carbon is the horizontal 
one. Later when in the prosecution of studies raise the current 
to one of 15 or even 20 amperes. Move the lens Ci backwards 
and forwards, at the same time holding a piece of dull black, 
glass, dull black paper, or a piece of ground glass in front of the 
slit, until a position is obtained which projects an image of the 
arc of maximum brightness upon the black screen and of such a 
size as to completely fill the slit opening. Set the slit so that 
the micrometer screw G is up as shown in the figure, and adjust 
the opening to about i millimeter by 1.5 millimeters, its length 
being horizontal. Now hold a black screen against the end of T 
and move C2 back and forth until a very bright and sharp image 
of the slit is obtained, adjusting Ci again slightly if necessary. 
Next hold the black screen so that its surface lies in the plane 
of the optic axis of the observing microscope and adjust the 
objective C3 so that a very bright, uniform spot of light a little 
less than i millimeter in diameter is obtained. Turn the fine 
adjustment V2 until the spot of light falls in the optic axis of M. 
For the final adjustment of the apparatus the cell may be filled 
with a liquid which contains colloids yielding brilliant diffraction 
patterns or with a slightly alkaline solution of fluorescein. The 
path of the illuminating beam is thus easily seen. Focus upon it, 
using a low power objective and No. i eyepiece and by means of 
Vi and V2 adjust the beam so that it passes through the center 
of the field as a narrow thread of light with its minimum diameter 
at the center of the field. Replace the material employed for ad- 
