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POPULAR SCIENCE REVIEW. 
stood that this small box or dark chamber performs a double office, 
depending upon the nature of the operation to be performed. To facilitate 
the operations of the photographer, this box or dark chamber is made to 
work in guides or dovetailed grooves, so that it may be easily removed 
from the camera and replaced when required. Another improvement 
consists in placing behind the lens, and in front of the negative, a stop 
with a very small aperture, in contradistinction to the large apertures of 
the ordinary stops. The patentee finds by experience that, for producing 
good results in making micro-photographs, the aperture of the stop should 
not exceed the fiftieth part of an inch in diameter, and that, in good lights 
and under favourable circumstances, a much smaller aperture may be 
advantageously employed. Another improvement consists in adapting to 
the object end of the camera a focussing lens, which is screwed on to the 
small removable box or dark chamber, and is adjusted by means of a 
sliding tube. 
Photogenic Pictures. — Mr. W. ClarTc, patentee. — This invention relates 
to a photogenic process, whereby a positive image may be obtained direct 
from a positive by the employment of ammoniacal salts, combined with the 
organic matter, and also by the precipitation of the following metallic solu- 
tions, viz. : salts of silver, copper, iron, nickel, mercury, gold, palladium, 
platina, lead, or tellurium, which are precipitated by means of hydro- 
sulphates of ammonia, potash, or soda. The salts of silver, bismuth, or 
lead, are precipitated by means of hydro-sulphuric acid, and the salts of 
mercury by hydro-chlorate of tin. The salts of bismuth may also be 
precipitated by means of nutgall, gallic or tannic acids, and the salts of 
iron by means of the same agents last mentioned. The inventor takes, 
for example, the sulphate of iron precipitated by means of tannic acids. 
Stereoscopic Apparatus. — Mr. H. Swan, patentee. — According to this 
invention, the patentee combines stereoscopic pictures with pieces of glass 
or transparent crystal of suitable form, in such manner that the pictures, 
which are in fact depicted on the exterior of the glass or crystal, or on 
surfaces placed in contact with, or at a small distance from them, shall 
produce an image apparently solid and imbedded in a glass or crystal. 
Stereoscopes. — Mr. S. Russell, patentee. — In performing this invention, 
an instrument is constructed in the form of a box, suitable for containing 
when out of use a number of stereoscopic slides or pictures. The instru- 
ment is closed by a sliding or other suitable cover when out of use, and 
on the interior and against one side mirrors are fixed. The bottom of the 
box may be made to slide also, so that when in use a stereoscope may be open 
both at top and bottom. The lenses or eye-pieces are fitted in apertures in 
the lower part of the opposite side of the box, this part of the side being 
suitably inclined to the plane of the mirrors. The stereoscope pictures or 
slides are, when about to be observed, placed in suitable grooves or holders 
opposite to the mirrors, and on the side where the lenses or eye-pieces are 
applied, and are held in a position inclined to the plane of the mirrors. 
By this arrangement no reflector is required to throw light on the picture, 
but the light falls directly on it, so as to illuminate it thoroughly. 
Manufacture of Paper. — Mr. G. E. Amos, patentee. — In carrying 
out this invention, the knots and other extraneous matters which accu- 
