other, illustrates an instance where the range of vision is not the same;
but I contend that the stereoscopic effect is then _confined_ to five {349}
houses and five machines, otherwise MR. WILKINSON'S supposititious case
(_ibid._), of all machines in one, and all houses in the other, might be
considered as stereoscopic.

In concluding this very lengthened and, I fear, tedious reply, I beg to
assert that I am most willing to recant any proposition I may have put
forth, if _proved_ to be erroneous; but I must have proof, not mere
assertion. And farther, my willing thanks are always tendered to any one
kind enough to correct an error.

GEO. SHADBOLT.

_Mr. Pumphrey's Process for securing black Tints in Positives._--The
importance that appears to be attached by some of thy correspondents to the
stereoscopic appearance of photographs, induces me to call the attention of
those who may not have noticed it to the fact that, as all camera pictures
are monocular, they are best seen by closing one eye, and then they truly
represent nature; and the effect of distance (which so often appears
wanting in photographs) is given with marvellous effect, so well indeed as
to render the use of a stereoscope unnecessary. Like other photographers, I
have been long seeking for a method, easy, cheap, and certain, for
obtaining the black tints that are so highly prized by many in the French
positives; and having at last attained the object of my search, I lose no
time in laying it before my fellow-operators.

I obtain these results with a twenty-grain solution of nitrate of silver, a
fact that will, I think, commend the plan to most operators. Thou wilt be
able to judge of the result from the inclosed specimen.[7] I use Canson's
paper, either albumenized or plain (but the former is far preferable). If
albumen is used, I dilute it with an equal measure of water, and add half a
grain of common salt (chloride of sodium) to each ounce of the mixture.
This is applied to the paper with a soft flat brush, and all bubbles
removed, by allowing a slender stream of the mixture to flow over its
surface: it is then hung up to dry, and afterwards the albumen is
coagulated with a hot iron. If the paper is used plain, a solution of
common salt (half a grain to one ounce of water) is placed in a shallow
tray, and the paper floated on its surface for a minute, and then hung up
to dry. Excite, in either case, with an ammonio-nitrate of silver solution
(twenty