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POPULAR SCIENCE REVIEW. 
photographic and microscopic manipulation as may be obtained 
in the ordinary treatises on those subjects. 
Camera . — To begin with the camera — which may be described 
as the dark chamber, extending from the object-glass of the 
microscope to the screen on which the image is focussed. A 
stout well-seasoned board, some eight feet in length by fifteen 
inches in breadth, is selected as a basis of operations (A). This 
is thoroughly blackened on its upper surface, and fitted with 
grooves (strips of wood fixed with screws), in which the several 
supports of focussing screen, microscope, and illuminating appa- 
ratus, may run evenly and with accuracy. The woodwork of 
an ordinary camera, or that portion of it which holds the focus- 
sing glass (C), may readily be obtained without the lens, and at 
a trifling cost. This is rigidly fixed to a light wooden block (B) 
at such a height as to place the centre of the focussing screen 
in the axis of the microscope, which is levelled horizontally, and 
secured by movable clamps to a sliding board at the opposite 
end of the base-board (A). 
Two blackened slips of wood diverging from one another are 
connected by cross-pieces, so as to form a light triangular 
framework (F); and this, resting with its base on the camera (C), 
and with its apex on the microscope, affords support to a double 
fold of cotton velvet (Gf), which (pile side inwards) is thrown 
over all. The cloth is then carefully tucked in at all points, 
and its junction with the microscope effected by a layer of 
cotton wool closely applied to the tube, round which the velvet 
is readily secured by an indiarubber band or thread. Every 
screw-head an'd reflecting portion of brass-work must be 
thoroughly coated with a dead black varnish, and when the 
necessary diaphragms have been inserted, the camera is ready 
for use. The whole may be supported on trestles (T), or 
mounted on an ordinary table; it will practically, however, be 
found convenient to place it in some spare room, if such is 
available, where all may be left undisturbed from day to day ; 
for much time is lost, and much experimental work wasted, if 
the whole has to be arranged de novo for every evening’s work. 
Many improvements might be suggested on the form of camera 
which I have described, such as the bellows arrangements of 
Professor Pood* and of Dr. Maddox, or some modification of 
Mr. Highley’s long box camera ; but these are attended with 
expense, and, though they add to the convenience, do not in any 
way increase the efficiency of the instrument. 
Focussing Screen . — The focussing screen is best made of a 
piece of good glass, coated with collodion, sensitised in the usual 
way, and protected by a solution of tannin. The film thus 
* Transact. Microscopic . Soc. vol. ii. N.S. 
