viz. taking the picture at once in the
camera, and it is very possible that it can be made perfect. A small
quantity of chromate of potash, about one grain to three ounces of solution
of iodide of iron, gives a little more force to the picture.

I find the nitrate of lead a very useful salt in iodizing paper. Six grains
of the salt to the ounce of water, and tincture of iodine added till a pale
yellow, will give additional sensitiveness to iodized paper, if the sheets
are floated upon the solution. This will shorten the time in the camera
nearly five minutes; but it requires care, as it is apt to solarize.

A weak solution of iodide of iron has also the same effect, and, if blotted
off at once, it will not blacken by the use of gallic acid.

WELD TAYLOR.

Bayswater.

_Stereoscopic Angles._--When I last addressed you, I fancied I should set
the stereoscopic-angle question at rest. It appears, however, that MR. G.
SHADBOLT is unconvinced, and as I alone (to the best of my knowledge) have
defined and solved the problem in relation to this subject, you will
perhaps allow me to offer a few words in rejoinder to MR. S.'S arguments
which, had that gentleman thought more closely, would not have been
advanced. This is also requisite, because, from their speciousness, they
are likely to mislead such as take what they read for granted. MR. S. says
that when the stereographs are placed at the same distance from the eyes as
the focal length of the lens, that 2-1/4 inches is the best space for the
cameras to be apart; and that were this space increased, the result would
be as though the pictures were taken from models. To this I reply, that the
only correct space for the cameras to be apart is 2-1/2 inches (_i. e._ the
space usually found to be from pupil to pupil of our eyes), and this under
every circumstance; and that any departure from this must produce error. As
to the model-like appearance, I cannot see the reason of {276} it. Next MR.
SHADBOLT says, and rightly, that when the pictures are seen from a less
distance than the focal length of the lens, they appear to be increased in
bulk. But the "obvious remedy" I pronounce to be wrong, as it must produce
error. The remedy is nevertheless obvious, and consists in placing the
stereographs at the same distance from the eyes as the focal length of the
lens. But, if this cannot be done, it were surely better to submit to some
trifling exaggeration than to absolute deformity and e