146 
PRACTICAL PHOTO-MICROGRAPHY. 
clouds, or trees, or anything coming in the field and in 
the focus of the lens, a piece of ground-glass must be 
put about two inches behind the negative. 
The amount of enlargement is regulated by the 
distance of the lens from the small plate, and the focus 
is adjusted on the ground-glass of the large camera, or 
on a piece of plain-glass placed pro tempore in the dark 
slide, the paper being put in when the focus is adjusted. 
If the image does not fall on the centre of the paper 
this is corrected by moving the rising or traversing 
front of the larger camera carrying with it the small 
camera. Of course it is necessary that the junction of 
the two cameras shall be light-tight. A piece of velvet 
will effect this in the simplest manner. 
If we only wish to enlarge to such size as can be 
taken by our photo-micrographic camera, we have at 
command an apparatus even simpler. In fig. 33 we 
show our photo-micro camera, its support carrying an 
easel for the small negative. This easel has a certain 
amount of vertical and horizontal motions, and will 
carry, if required, a quarter-plate negative. The nega¬ 
tive is simply illuminated by diffused daylight, and 
“ copied,” but the lens is placed at such a distance from 
the negative and from the sensitive surface that the 
size of the image is about doubled—in diameters—on 
the paper. In place of the safety cap on the front of 
the camera, used in photo-micrography, a lens flange is 
adapted taking our short-focus photographic lens. The 
accurate focus is got by sliding the back of the camera 
in the usual way. This apparatus is of great value in 
