THE history of photography is a curious one. It shows how important discoveries are the outcome, not of one mind, but of the investigations of numberless men, working entirely independently of each other, and to ends altogether diverse. It falls to one man perhaps, by a lucky hit, to put the finishing touch to an edifice at which others may have been working for years, but who are liable to be forgotten in the success and fame of the one who achieves the completion of the struc ture. This is peculiarly the case with photography.
It has been observed that the tanning of the skin by exposure to the sun’s rays is as much a photographic action as is the blackening of luna cornea, or horn silver, the observation of which may be said to have been the first step in the science of photography. This horn silver is found in the mines of Freiberg. It is a vitreous, dully shining silver ore, and consists of silver and chlorine in chemical combination, and hence is known to science as chloride of silver. It can be artificially produced by passing chlorine gas over metallic silver. In its native state horn silver is completely colourless, but so soon as it is exposed to the light of day it in the course of a few minutes assumes a violet tint.
This effect of light upon Luna cornea appears to have been first bbserved by the alchemist Fabric’s in 1556, and long after his time it attracted the attention of men of science, although without leadin to any practical results.
In another substance containing silver this phenomenon is still more apparent. If silver be dissolved in nitric acid, and the solution be then evaporated, a solid mass of crystals is obtained. This is nitrate of silver, which fuses readily and destroys organic matter. Hence its use as a corrosive agent under the name of lunar caustic. Anything sprinkled with a solution of it very soon assumes a dark colour.
Many persons must have observed the blackening of paper under the action of lunar caustic, in which lay the primary secret of photography, and yet it was long years before any one thought of the uses to which it might be applied in the production of pictures by means of light.
The first person of whom we have any record who attempted to turn to account this property of silver nitrate to darken under the influence of light appears to have been a German physician, Johan Heinrich Schultze, of Halle, who, in 1727, attempted by means of written characters upon a surface prepared with a mixture of chalk and a solution of silver nitrate to take copies therefrom on paper that had been made translucent. The experiment, however, attracted very little attention, and probably was not very successful. Nothing material was added to these results until, in 1777, the famous Swedish chemist, Charles William Scheele, took up the discovery of Fabricius, and applying combined chemical and spectrum analysis to the science of photography, found that the violet rays of the spectrum act more energetically upon silver chloride than the blue, yellow, or red rays, or in other words, than the less refrangible rays. He thus proved that the rays of light are not all alike chemically active.
These results were confirmed a few years later by Senebier, who found that the violet rays in fifteen seconds blackened silver chloride as much as the red rays did in twenty minutes.
Scheele, however, went further than this. Exposing silver chloride to the action of sunlight under water, and when the white salt had darkened, pouring away the water and adding a little silver nitrate, he found a white substance was formed which proved to be silver chloride (caused by the silver nitrate combining with chlorine dissolved in the water). He thus demonstrated that the effect of sunlight upon chloride of silver is to decompose it, and so compel it to give up a part if not the whole of its chlorine.
This important discovery was carried still further in 1801 by Ritter of Jena, who demonstrated the existence of rays lying beyond the violet limit of the solar spectrum, and that they too had the power of darkening silver chloride.
Ritter also announced “that the red rays have the property of undoing the work effected by the violet; ” but he appears to have misunderstood the cause of the action. Similar results were obtained by Wollaston, the English chemist, in 1803. He found that gum guaiacum, when exposed to the influence of the blue rays, became changed in colour, and that on exposing those altered portions to the red rays the original tint was restored.
It is claimed by the French that the first actual photograph was taken by Professor Charles, who, struck with the property possessed by silver salts to blacken in contact with light, made some interesting experiments in a course of lectures on physics delivered by him at the Louvre in 1780. By means of a strong ray of light he threw the silhouette of one of his pupils upon a sheet of paper that had been saturated with chloride of silver. The paper, under the action of the light, blackened immediately at those parts which were exposed to the sun’s rays, while it remained white in those parts where the shadow fell, so that the figure of the youth was shown in white upon a black ground. But as soon as the shadow was withdrawn, the white, exposed to the sun’s rays, began to darken. M. Charles, however, left no account of his process, and considerable doubt has been thrown upon the reported achievement.
While up to the end of the eighteenth century the problem of drawing by light was still an unsolved one, it is curious to note that, among the hints and foreshadowings of photography that have been collected, one Frenchman made so apt a guess at sun-picturing that it amounted almost to a prophecy. The genius in question, Tiphaigne de la Roche, in the year 1760 published a book which he called ” Giphantie ” (an anagram of his name), and in which, amongst other Munchausenisms, he describes a method whereby a strange people, in whose land he is sojourning, produce pictures of objects. “You know,” says his guide, “that rays of light reflected from different bodies form pictures, paint the image reflected on all polished surfaces, for example, on the retina of the eye, on water, and on glass. The spirits have sought to fix these fleeting images; they have made a subtle matter by means of which a picture is formed in the twinkling of an eye. They coat a piece of canvas with this matter, and place it in front of the object to be taken. The first effect of this cloth is similar to that of a mirror, but by means of its viscous nature, the prepared canvas, as is not the case with the mirror, retains a facsimile of the image. The mirror represents images faithfully, but retains none; our canvas reflects them no less faithfully, but retains them all. This impression of the image is instantaneous. The canvas is then removed and deposited in a dark place. An hour later the impression is dry, and you have a picture the more precious that no art can imitate its truthfulness.” *
It is hardly possible to read this strange foreshadowing of the photographic art without feeling that De la Roche had been gazing upon the magic pencillings of the camera obscura, and that in imagination he had realised the problem which investigators a few years later were trying to solve.