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YEAR 1844.

By J. T. Towson, Esq., F.R.G.S.


IN attempting to trace the progress of the Science of Photography, it is necessary to notice several distinct classes of discoveries, the combination of which was necessary to bring about its present advancement.

The mechanical department had its origin at the latter part of the sixteenth century, when John Baptist Porta invented the camera, by means of which instrument the rays of light are arranged so as to produce a picture of the objects from which those rays are reflected. The science of Chemistry in various ways contributed to the production of a photographic picture. In the first place, the action of light produces a change in the affinities of the salts, or other materials of which the photographic preparation consists, for other chemical preparations afterwards employed. This is sometimes attended by a change of the colour of the material acted on by light, but not always so. In this latter case, the developing process is necessary, and, under all circumstances, the fixing process is required to render the picture permanent. The first chemical discovery leading to the science of Photography was made by Scheel in 1777, who found that the solar ray darkened the chloride of silver. In 1801 Ritter discovered that on the nitrate and other salts of silver a similar effect was produced.

Wedgwood two years afterwards applied the last-named discovery to photographic purposes. He applied the solution of salts of silver to leather, and by this process he obtained copies from paintings on glass. But he remarks that-" No attempts that have been made to prevent the uncoloured parts "of the copy or profile from being acted upon by light, have as yet been successful. The images, formed by means of a "camera obscura, have been found to be too faint to produce "in any moderate time an effect upon nitrate of silver."


Although thus early in the present century advances were made in the science of Photography, it could not be said to exist as an art previously to 1839. It is true that Niepce, as early as 1814, produced pictures in the camera; and in 1829 Daguerre produced, on sheets of silver-plated copper, his pictures known by the name of Daguerreotype. But these discoveries remained hidden to the men of science and art until 1839, when the French Government purchased these



Immediately on the publication of the discoveries of M. Niepce and M. Daguerre, several English men of science, who had pursued researches in the same direction, were encouraged to exert greater diligence. They received further stimulus to pursue these investigations from the fact that the English artist was deprived, by a patent, of the endowment which the French government had bestowed on "the world "of science and of art." This ultimately led to the English School of Photography, that has now superseded the discoveries of Daguerre.

The processes of Niepce and Daguerre brought to light two departments of Photography not previously known-the developing and fixing processes. By their methods the impression made whilst the tablet was in the camera was scarcely, if at all, visible, but was made so by the developing process.

Niepce employed tablets of glass or of silver plated on copper, covered with a thin coating of asphaltum. These were exposed from six to eight hours in the camera, when a faint outline only was visible. The development was accomplished by a solvent, that acted less readily on the asphaltum that had been exposed to light, than on that which had remained comparatively in shade.

The process of Daguerre was far more complicated. All his pictures were imprinted on silver plated on copper, and consisted of five operations; and most of these were very delicate, and required very skilful manipulation. Still for several years it defied competition. Perhaps, however, the greatest ultimate value of the discoveries of Daguerre consisted in directing the attention of the photographers generally to the fact, that imperceptible impressions may be made in the camera, which certain developing re-agents, when applied, would render visible.

The "fixing process" of Daguerre may also be regarded as one of the greatest discoveries in connection with Photography, The other methods adopted, previously to his discovery being known, may be described as the rendering that part of the preparation not acted on by light less sensitive, rather than in absolutely protecting it from the further influence of the solar ray. Daguerre's method was by the employment of a solution of hyposulphite of soda, by which he dissolved and thus removed the salts of silver not acted upon by light, rendering the picture absolutely fixed, as far as the further action of light is concerned. The materials employed by others at this time were common salt, iodides or bromides, which converted the whole of the salts of silver not acted on by light into a chloride, iodide or bromide as the case may be. Each of these salts, uncombined with other salts of silver, is far less sensitive than a preparation in which various salts of

silver are present in determined proportions. The hyposulphite of soda has been employed down to the present day for fixing photographs; either this salt or the cyanide of potassium is, I believe, now universally employed for that


Down to the year 1840 still-life objects alone could be depicted by Photography. When Daguerre published his process, a period of twenty minutes was required to obtain a good picture of an object; and the other photographic processes then known required even a longer period of time. Several chemists and others, during this and the former year, had laboured in endeavouring to shorten the time required to produce a photograph. Amongst others thus employed at the period named were Talbot, Claudet, Goddard, Draper, Herschel and Hunt. Professor Hunt and myself pursued this object conjointly during the whole of 1839. I directed my attention principally to the mechanical department-the improvement of the camera for photographic purposes; and Mr. Hunt was principally employed in discovering new chemical preparations applicable to Photography, and in rendering those already known more sensitive. Our labours were both, to some extent, crowned with success. In my experiments on the comparative value of lenses, I found that the quickest were those made of flint glass, and that the thinner the glass the more rapid was the process; and that achromatic glasses were much slower than simple lenses, but that the latter gave a confused and indistinct picture. This I discovered to arise from the luminous ray being subject to a less amount of refraction than the chemical ray ;* that with a lens or lenses of twelveinch focus by moving the plate or paper a quarter of an inch nearer the lens, a picture was produced quite equal to that

* See the London and Edinburgh Philosophical Magazine, for November, 1839, page 382, and Hunt's Manual of Photography (1854), page 169.

obtained by means of an achromatic lens,* and in less than one-twentieth the time.t

I intimated, when I published this discovery, that the use of non-achromatic lenses of large dimensions might lead to the application of Photography to the purpose of portraiture.‡ This expectation was realized, as is shown in the following quotation from the remarks of Professor Hunt§ :-" Dr. "Draper, of New York, acting on the suggestions of Mr. "Towson, relative to the adjustment of the focus, succeeded "in accelerating his process so far as to obtain portraits from "6 the life."

About the same time I made many experiments with cameras having mirrors instead of lenses. These cameras were very quick, and gave a very distinct picture in the centre of the field, which, however, was very limited. Whilst we were thus successful, Goddard and Claudet were still more fortunate in their attempts to accelerate the process by improvements in the chemical department. Goddard discovered that the use of a small amount of bromine, mixed with the iodine, greatly reduced the time necessary to make the required impression; and Claudet, about the same time, discovered that the introduction of small portions of liquid chlorine produced a

Claudet shows, in the London and Edinburgh Philosophical Magazine, 1844, that the luminous and chemical foci were not of the same length, even with achromatic lenses. Achromatic lenses are, however, generally used at present in this country; but in America a combination of simple lenses. The lenses of some very quick cameras, used in this country for taking portraits of children, are similar to the one I described in 1839.

+ The chemical ray has since been denominated "actinism."

The London and Edinburgh Philosophical Magazine, November, 1839, page 385.

§ Ibid., September, 1840 and 1844. Also, Hunt's Manual of Photography, page 96.

|| Hunt's Manual of Photography, page 99, where a drawing of my reflecting camera is also given. In taking a Daguerreotype, or any other positive picture, in the camera, the reflector had the advantage in depicturing the right for the right and the left for the left, whereas in the refracting camera right and left were reversed; but this defect is corrected by printing positive pictures from negatives taken in the refracting camera.

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