otherwise laborious, and often mechanical, task of drawing in detail
from nature and from the human figure.

"To the physician, to the naturalist, and to the man of science, the
uses of photography are various and important, and already the
discoveries which have been directly due to this modern art are of
stupendous utility.

"To the metaphysician, its uses may be sufficiently gleaned from the
applications considered in the preceding pages. But to all these
classes of men the photographic art derives its chief glory from its
application to the stereoscope; and if, for elucidating the principles
of vision by means of this application, we have in any degree given a
stimulus to the practice and improvement of the photographic processes,
our pains have been happily and fruitfully bestowed."

_Muller's Processes._--Would you inform me, through the medium of "N. &
Q.," what manufacture of paper is best adapted to the two processes of Mr.
Muller? I have tried several: with some I find that the combination of
their starch with the iodide of iron causes a dark precipitate upon the
face of the paper; and with those papers prepared with size, there appears
to me great difficulty (in his improved process after the paper is
moistened with aceto-nitrate of silver) to procure an equal distribution of
the iodide over its surface, as it invariably dries or runs off parts of
the paper, or is repelled by spots of size on the paper when dipped in the
iodide of iron bath.--A reply to the foregoing question would greatly
oblige

A CONSTANT READER.

Essex.

_Positives on Glass._--Sometimes, when your sitter is gone, and you hold
your portrait up to the light to examine its density, you find in the face
and other parts which are dark, so viewed, minute _transparent_ specks,
scarcely bigger than a pin's point. When the picture is backed with black
lacquer, you have consequently small _black_ spots, which deform the
positive, especially when viewed through a lens of short focus. A friend of
mine {452} cures this defect very easily. After having applied the amber
varnish, he stops out the spots with a little oil-paint that matches the
lights of the picture; of course the paint is put upon the varnished side
of the glass. When the paint is dry, the black lacquer is carried over the
whole as usual.

T. D. EATON.

Norwich.

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