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386
TROUBLES IN DRAWING
[On. 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 specimen. 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 (ยง 314, 533).
(3) In drawing with the microscope where the substage condenser 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 OUTFIT AND VERTICAL CAMERA ARRANGED FOR PHOTO-MICROGRAPHY.
(From The Microscope}.
The apparatus is set up on a long table 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., iJ/2 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 100 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 capacity of the photo-micrographic camera it is possible to use an ordinary camera, (fig. 117119), then even quite large objects 50 to 60 mm. long, can be magnified considerably. 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.