386
TROUBLES IN DRAWING
ICh. X
likely to arise is the lack of a brilliant picture on the drawing paper
owing to the light in the room. Remember that to get a brilliant
image the light must come to the eyes from the drawing surface
only, and the drawing surface must receive no light except that
from the sj>ecimen. The weaker the light and the greater the
magnification the darker must the room be.
(2) In drawing from negatives or lantern slides remember that
it is necessary to have a condenser somewhat larger than the
diagonal of the object to be drawn (§314, 533).
(3) In drawing with the microscope where the substage con¬
denser is used the condenser must be in the exact position to give
the best results. If the slide is thick the condenser is a little higher
Fig. 219. Micro-Projection Oitfit and Vertical Camera Arranged
for Photo-Micrography.
(From The Microscope).
The apparatus is set up on a long tabic or on two tables placed end to end.
The vertical camera (fig. 217) is placed horizontally and the bellows reversed.
For illumination a petroleum lamp with large flat wick (38 mm., ijtj in.)
answers well.
Objects 50 to 60 mm. in diameter may be fully illuminated with the face of
the flame, the lamp being i to 2 centimeters from the condenser. For powers
of ioo to 150 diameters the flame is turned obliquely or edgewise, and placed
5 to 6 centimeters from the condenser. The position shown in the picture
above is for high power work. No water-cell or specimen cooler is needed.
A light-tight connection is made with the large tube of the microscope by a
double sleeve like that employed by Zeiss for the microscope. With low
magnifications no ocular is used, and the objective is placed in the end of the
camera. If one desires to make pictures of a size above the capacitv of the
photo-micrographic camera it is possible to use an ordinary camera, (fig. 117—
119), then even quite large objects 50 to 60 mm. long, can be magnified con¬
siderably. The petroleum lamp has some advantages over daylight as the
lamp gives an illumination of constant intensity. It is available during the
entire 24 hours of the day, and in all seasons.