PHOTOGRAPHY, the most widely practised and most versatile of the pictorial arts, is also the youngest. Seventy years ago its very name was unknown, and only a few crude principles existed in the transactions of learned societies. And yet its history might be traced back for many generations. To no single individual belongs the honour of the invention. A long chain of discoveries, made by workers at periods long distant from each other, extends right down to our own day; the sum of these combined makes up photography as now practised.

In vain may we seek to find who first observed that certain chemical substances are changed in colour or decomposed by the action of light The fact was not unknown to the ancients. It is mentioned by Paracelsus. Boyle is usually given credit for having described some of these changes in terms of modern science. Thomas Wedgwood, about 1791, applied the idea to practice by coating paper with nitrate of silver and placing on it various objects, such as fern-leaves, etc.; when exposed to light the objects were shown in outline on a blackened ground. Sir Humphry Davy published the results of these investigations in 1802, but no method of fixing the image satisfactorily was then known. A few years later Nicephore Niepce, a French experimenter, made similar sun-pictures on glass and metal plates with bitumen dissolved in petroleum, and also with guaiacum, which became insoluble on exposure to light; these "heliographs" were permanent. An early example made in 1824, a copy of a portrait of Cardinal d'Amboise, may be seen in the museum at Chalons-sur-Saone.

John Baptist Porta, in the seventeenth book of his Magia Naturalis, published about 1550, directs how to make a small aperture in the shutter of a perfectly dark room; the light from this opening, falling on a white screen, gave an image of the external landscape, but reversed. He afterwards improved this image by inserting a small convex lens in the opening. Hence grew up the camera obscura of our grandfathers.

The legend runs that about the year 1820 a lady called to consult one of the leading men of science in Paris. She complained that her husband had been seized with the strange idea that the beautiful but fleeting pictures seen in the camera obscura could be made permanent. All the remonstrances of his friends were vain. What she desired to know was, whether there was the slightest hope of his succeeding in a project which was gradually absorbing all his means, or whether it must be treated as a mere delusion. The great man temporised with his fair visitor - which was just as well - for the name of her husband was Daguerre, and his strange idea was a few years later to become a fact of everyday knowledge.

Daguerre became acquainted with Niepce, and a partnership was arranged between the two. Niepce died in 1833, and Daguerre purchased from his son the right to omit any mention of him in connection with the process, known as Daguerreotype, which he published in 1839. It consisted in subjecting a surface of metallic silver (obtained in practice by thickly plating with silver a sheet of copper) to the fumes of iodine. The thin film of silver iodide thus obtained was sensitive to light, and was exposed in the camera. The image became visible by the aid of mercury vapour, and was then fixed in common salt, until Sir John Herschel advised the adoption of hyposulphite of soda. Altogether this year 1839 was a significant one. On the 7th of January, M. Arago communicated the news of Daguerre's success to the Academic des Sciences, and on the 25th of the same month Faraday described to the members of the Royal Institution Fox Talbot's "Method of Photogenic Drawing."

The practical difference between the two inventions was that the Daguerrotype presented a finished picture on metal in the lights and shades of nature, but one which could not be copied without going through the whole expensive process over again. Talbot's process produced a paper negative in which the lights appeared reversed - the whites as black and the blacks as white. From this any number of copies were made, with the colour-shades correctly rendered, by simply placing the negative in contact with a fresh piece of the prepared paper in a printing frame. The sensitive salts were chloride and iodide of silver, and a solution of gallic acid was used in development. Afterwards the paper was rendered more transparent by the application of white wax. This process continued to find favour till about 1855, when it was supplanted by the collodion wet plate. Meanwhile, albumen paper for securing finer gradation in printing, and the first recorded method of photo-etching on metal had also been introduced by Fox Talbot.

That Photography, even under these elementary conditions, had already enlisted the sympathies of a considerable body of workers was shown when the Photographic Society of London was founded in 1853 with Sir Charles Eastlake as president; it is now an incorporated body, and known as the Royal Photographic Society of Great Britain. A year later the first number of the British Journal of Photography saw the light.

In 1851 Frederick Scott Archer published the details of his invention, which shortly afterwards was to come into general use as the wet-plate process. Glass replaced silvered copper or paper as a support for the sensitive salts; and the vehicle for these salts was a film of collodion. The effect of these changes was that a much shorter exposure to light was possible to secure a picture; either a positive or negative result might be obtained; and the crispness of effect and delicacy of detail far surpassed either the Talbotype or the Daguerrotype.