Hammersmith.
_Stereoscopic Pictures from one Camera._--Your correspondent RAMUS will
easily obtain stereoscopic pictures by either of the following
plans:--After the first picture is taken, move the subject, as on a pivot,
either to the right or left, through an angle of about 15°; then take the
second impression: this will do very well for an inanimate object, as a
statue; but, if a portrait is required, the camera, after taking the first
picture, must be moved either to the right or left, a distance of not more
than one-fifth of the distance it stands from the sitter; that is, if the
camera is twenty feet from the face of the sitter, the distance between its
first and second position should not exceed four feet, otherwise the
picture will appear distorted, and the stereosity unnaturally great. Of
course it is absolutely necessary in this plan that the sitter do not move
his position between the taking of the two impressions, and also that the
distance between him and the camera be the same in both operations. {49}
In reply to the very sensible inquiry of SIMPLICITAS, there is an essential
difference between the calotype of Talbot and the waxed-paper process, the
picture in the first being almost entirely superficial, whilst in the
latter it is much more in the body of the paper; this causes the
modification of the treatment. A _tolerably-strong_ solution of (A_9O NO_5)
nitrate of silver is required to decompose the (KI) iodide of potassium,
with which the paper is _saturated_, in any reasonable time, but if this
were allowed to dry on the surface, stains would be the inevitable result;
therefore it is floated in distilled water, to remove this from the
_surface_; and it seems to me that the keeping of the paper depends on the
greater or less extent to which this surface-coating is removed. There can
be no doubt that the paper would be far more sensitive, if used
immediately, without the washing, simply blotting it off; but then the
great advantage of the process would be lost, viz. its capability of being
kept.