_History of Photographic Discovery._--Without entirely agreeing with the
opinion expressed to us a few days since, by an eminent scholar and most
original thinker, that photography was destined to change the face of the
whole world; we have little doubt it is destined to produce some striking
social effects. Its history is, therefore, an interesting one, and the
following extract from a paper "On some early Experiments in Photography,
being the substance of a Letter addressed to Robert Hunt, Esq., by the Rev.
J. B. Reade, M.A., F.R.S.," from the _Philosophical Magazine_ for May,
1854, seems, in that point of view, so important, that we have transferred
it to "N. & Q."
"I may assume that you are already aware, from my letter to Mr. Brayley of
March 9, 1839, and published in the _British Review_ for August, 1847, that
the principal agents I employed, before Mr. Talbot's processes were known,
were infusion of galls as an accelerator, and hyposulphite of soda as a
fixer.
"I have no doubt, though I have not a distinct recollection of the fact,
that I was led to use the infusion of galls from my knowledge of the early
experiments by Wedgwood. I was aware that he found _leather_ more sensitive
than _paper_; and it is highly probable that the tanning process, which
might cause the silver {525} solution to be more readily acted upon when
applied to the leather, suggested my application of the tanning solution to
paper.
"In your own history of the photographic process," says Mr. Reade,
addressing Mr. Hunt, "you say, 'the discovery of the extraordinary property
of the gallic acid in increasing the sensibility of the iodide of silver
was the most valuable of the numerous contributions which Mr. Talbot has
made to the photographic art.' It is nevertheless true, as stated by Sir
David Brewster, that 'the first public use of the infusion of nut-galls,
which is an _essential element_ in Mr. Talbot's patented process, is due to
Mr. Reade;' and in my letter to Mr. Brayley I attribute the sensitiveness
of my process to the formation of a gallate or tannate of silver. I need
scarcely say, that among various experiments I tried gallic and tannic acid
in their pure state, both separately and mixed; but the colour of the
pictures thus obtained with the solar microscope was at that time less
pleasing to my eye, than the rich warm tone which the same acids produced
when in their natural connexion with solutions of vegetable matter in the
gall-nut. This organic combination, however, was more effective with the
solar microscope than with the camera, though the lenses of my camera were
five inches in diameter. It is probable enough that the richer tone was due
to the greater energy of direct solar rays. In using the solar microscope,
I employed a combination of lenses which produced a convergence of the
luminous and photogenic rays, together with a dispersion of the calorific
rays, and the consequent absence of all sensible heat enabled me to use
Ross's cemented powers, and to make drawings of objects inclosed in Canada
balsam, and of living animalcules in single drops of water. The method I
employed was communicated to the Royal Society in December, 1836, and a
notice of it is contained in the 'Abstracts.'
"You inform me that some persons doubt whether I really obtain _gallate of
silver_ when using an infusion of gall-nuts, and that one of Mr. Talbot's
friends raises the question. It is sufficient to reply, that though gallic
acid is largely formed by a long exposure of an infusion of gall-nuts to
the atmosphere, as first proposed by Scheele, yet this acid does exist in
the gall-nut in its natural state, and in a sufficient quantity to form
gallate of silver as a photogenic agent; for M. Deyeux observes, that 'when
heat is very slowly applied to powdered gall-nuts, gallic acid sublimes
from them, a part of which, when the process is conducted with great care,
appears in the form of small white crystals.' M. Fiedler also obtained
gallic acid by mixing together a solution of gall-nuts and pure alumina,
which latter combines with the tannin and leaves the gallic acid free in
the solution; and this solution is found, on experiment, to produce very
admirable pictures. But what is more to the point, Mr. Brayley, in
explaining my process in his lectures, showed experimentally how gallate of
silver was formed, and confirmed my view of the sensitiveness of the
preparation. It is therefore certain that the use of gallate of silver as a
photogenic agent had been made public in two lectures by Mr. Brayley at
least two years before Mr. Talbot's patent was sealed.
"I employed hyposulphite of soda as a fixer. Mr. Hodgson, an able practical
chemist at Apothecaries' Hall, assisted me in the preparation of this salt,
which at that time was probably not be found, as an article of sale, in any
chemist's shop in London. Sir John Herschel had previously announced the
peculiar action of this preparation of soda on salts of silver, but I
believe that I was the first to use it in the processes of photography. I
also used iodide of potassium, as appears from my letter, as a fixer, and I
employed it as well to form iodide of lead on glazed cards as an
accelerator. Iodide of lead has of itself, as I form it, considerable
photographic properties, and receives very fair impressions of plants,
lace, and drawings when placed upon it, but with the addition of nitrate of
silver and the infusion of galls the operation is perfect and
instantaneous. Pictures thus taken were exhibited at the Royal Society
before Mr. Talbot proposed his iodized paper. The microscopic photographs
exhibited at Lord Northampton's in 1839 remained in his lordship's
possession. I subsequently made drawings of sections of teeth; and one of
them, a longitudinal section of a tooth of the _Lamna_, was copied on zinc
by Mr. Lens Aldous for Owen's 'Odontography.' I may say this much as to my
own approximation to an art, which has deservedly and by universal consent
obtained the name of Talbotype."
_Photographic Cautions._--Diffused light being one of the most common
causes of photographic failures, I beg to call the attention of your
readers to the construction of their cameras. Working with a friend, and
taking the same localities, using the same paper and chemicals, his
pictures have proved comparative failures, a general browning pervading the
whole, evidently the effect of light. Every inspection failed to discover
it, until the mode was adopted of putting one of the paper-holders in its
position as for taking a picture, then removing the lens, and, with the aid
of the focussing-bag, looking through the hole where the lens is applied,
when light became visible in many spaces, entirely accounting for these
failures. As many such cameras are now becoming made upon the same sliding
construction, every one should test his apparatus before he commences, for
such a one is entirely useless. Lately also the glass corners for collodion
plate-holders in the dark slides, have been by some makers replaced by a
sort of silver _looking_ wire, but possessing little of that metal. The
most minute portion of the copper in this wire coming in contact with the
excited collodion, produces a decomposition sufficient to spoil any
picture. These may appear trivial things to "make a note of," but as they
have caused much vexation to one who has had some photographic experience,
they may still more perplex a novice; and as you have done so much towards
making the science plain, I hope you will give them space in your
forthcoming Number.