best angle 1 in 10
when the sitter is 10 feet off, and for busts about 1 in 5 when placed
about 5 or 6 feet from the cameras. But I should be happy to receive
information from any of your readers concerning this important branch of
the photographic art. For months past I have been engaged in a series of
experiments in connexion with the subject, and wish for larger experience
than it is possible for any single operator to acquire for himself.

Mr. Fenton, I may observe, does not keep the cameras parallel in taking
landscapes, but inclines them so that the same object may occupy as nearly
as possible the centre of the ground glass plate.

Nor is it essential that perfect horizontality or parallelism of the
cameras should be maintained in copying trees. For buildings, however, it
is absolutely necessary that the cameras be kept straight.

I am sorry thus to trespass on your space, but being anxious, as MR.
WILKINSON says, to collect information from every source, and your
periodical being a happy medium for conveying and receiving instruction, I
am glad to avail myself of such a channel.

[Phi]. (2)

P.S.--Mr. Claudet has, I perceive, been awarded the prize given by the
Society of Arts for the best essay on the stereoscope. Can you, or any of
your readers, inform me whether this is likely to be published, and when
and at what price?

_Query respecting Mr. Pollock's Process._--In MR. POLLOCK's directions for
obtaining positives which appeared in "N. & Q." (Vol. vii, p. 581.), iodide
of silver is to be dissolved in a saturated solution of hypo. Can you give
me the quantity of iodide of silver to be dissolved, and the quantity of
the saturated solution of hypo. in which it is to be dissolved?

N. T. B.

_Gallo-nitrate of Silver._--Can you inform me what the true nature of the
decomposition is which takes place after a short time in the gallo-nitrate
solution of silver? and if there be any ready means of rendering the silver
it contains again available for photographic use?

SIR W. NEWTON, in the description of his calotype process, says: "Bring out
with the saturated solution of gallic acid, and when the subject begins to
appear, add the aceto-nitrate of silver solution." Which way of doing this
is the best,--mixing the two solutions together and applying them to the
paper; or applying the paper, when wetted with the gallic acid, to the
silver solution?

T. L.

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