44 PRACTICAL PHOTO-MICROGRAPHY. 
passes through the bottom of the box ; and the box is 
large enough to admit the worker’s head for focussing 
purposes. The whole front of the box opens, and the 
whole length of the “ camera ” is nearly 20 inches. 
The final focussing is done on plain glass at the top of 
the box, where the plate is put for exposure (fig. 12). 
The following is a description of an apparatus de¬ 
signed to fulfil three main desiderata : Photography of 
objects and substances requiring to be kept in the 
horizontal position ; very rapid exposures; and the 
rendering of objects undergoing more or less rapid 
changes, these changes being watched up to the instant 
of exposure. 
From fig. 13 it will be seen that in general the 
apparatus is that of Van Heurck, but for ordinary work 
the focussing is done by a counterpoised power actuated 
from a milled head A near the ground-glass and outside 
of the camera. The focussing cord passes round a 
pulley B, then round the fine adjustment screw of the 
microscope, then over other pulleys ; and the weight is 
an objective-box C filled to the proper amount with shot. 
This of itself makes an admirable vertical apparatus 
for ordinary work ; like Dr. Van Heurck’s apparatus, it 
has no available extension of camera-length, but the 
necessary magnification can be obtained by use of 
suitable objectives and oculars. The junction between 
tube and camera is made doubly—by a fitting on a short 
length of bellows inside the camera, and by a sleeve 
of velvet constricted by a rubber band. Centring, 
focussing, etc., are first done with the head inside the 
