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obtain an image of the desired size and focus- 
ing; 3°. Lighting and centring the object; 
4°. The obtaining of outlines for tracing upon 
the drawing-paper. 
Hig. 2. —Front view of the vertical camera. /, slotted brass 
guide, serving to support the upper part of the camera, and to 
indicate the enlargement or reduction; H, frame hinged to the 
table; /, board moving in the frame Z, and holding the came- 
ra; JV, iron bars attached to the bed of the camera (upon these 
presses the thumb-screw from the board J); QO, similar iron 
bars in the movable board (in the slot works a thumb-screw 
from the camera; these thumb-screws clamp the camera to the 
movable board); P, object-carrier on casters (this may be 
moved by the operator by turning the spools Q); Q, spools for 
the cords from the object-carrier. 
While the camera delineates rapidly, the 
image is liable to distortion. I believe opti- 
cians are agreed, that, in order to obtain cor- 
rect photographic images, the objective must 
be properly made, and the plane of the object 
must be parallel to the plane of the ground 
glass. Furthermore, as most of the objects in 
natural history have not plain surfaces, but are 
situated in several planes at different levels, 
there will be a liability of distortion from that 
cause also. ‘This may be rendered practically 
nothing, however, by using in the objective a 
diaphragm with a small opening. 
2°. By placing the camera on a long table, 
and a scale of some kind against the wall, the 
exact position of the oround glass for various 
SCIENCE. 
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sizes may be determined once for all. These 
positions are noted in some way (on the brass — 
guide, F, in the apparatus here figured). 
Whenever it is desired to photograph an object, 
natural size, for example, the ground glass ‘is 
fixed in the proper position indicated on the 
brass guide (fig. 2, #). Then, as the relative 
position of the objective and the ground glass 
cannot be varied, it is necessary, in focusing, 
to move the camera toward or away from the 
object, or the reverse. In order to do this, the 
camera is fastened to a board which moves 
in a frame by means of a screw (figs. 1, 2, J, 
Whenever the camera is to be moved 
considerably, — as to a position for twice nat- 
ural size from one giving an image of half 
natural size, — the position of the camera on 
the board is changed by loosening the two 
thumb-screws clamping it to the movable board 
(fig. 2, VW, O). The approximate position for 
the various sizes being once determined and 
noted, it is but a moment’s work to set the 
camera for any enlargement or reduction within 
its range. 
oe The object is placed on the horizontal 
stage, and so arranged that the lighting will 
give prominence to the parts to be especially 
emphasized. For a contrasting background, 
black velveteen for light, and white paper 
for dark, objects, have been found excellent. 
To get the object in the centre of the field of 
the objective, the stage bearing the object may 
be movable ; so that the operator, while looking 
at the image on the ground glass, may move 
the object in any desired direction by turning the 
spools on which are wound the cords from 
the movable stage (fig. 2). 
4°. If the photographic prints are to be used 
solely for outlines, the well-known blue prints 
so much used in engineering and architecture 
may be made. If, however, light and shade 
and fine details are to be brought out with great 
distinctness, either a silver or a platinotype 
print is preferable. In whatever way the print 
is made, it is blacked on the back with soft 
lead-pencil, put over the drawing-paper, and 
the outlines traced. Instead of making a print 
from the negative, one may get a tracing di- 
rectly from it on tracing-paper ; and this may, 
of course, be used in the usual way. Finally, 
if one possesses a camera, a tracing may be 
made of the image directly, without the aid of 
a negative. It is only necessary to substitute 
a piece of plain glass for the ground glass, and, 
after spreading upon it some fine tracing-paper, 
to trace the image. This is especially appli- 
cable to the enlargement or reduction of other 
figures. Smon H. Gace. 
