9. The story of photography is that of a dream come true - a fancy transmutted into fact.

Whoever was the first to wonder why the image of the summer clouds in a woodland pool, or his own face reflected in his shield of burnished copper, might not be fixed there - such a one was, in spirit, the first photographer. Around some such fancy, legends grew; of magic mirrors that would show scenes at a distance; of charmed basins that held, in the water that filled them, grewsome pictures.

10. Then came the practical people - still under the inspiration of the dream, working it out toward realization, in separate ways, until another, assembling the scattered materials combined them into a step, leading up to the door which at last was reached and opened on the wide and ever widening field.

11. Combining as it does the practical application of optics - the science of the nature, properties and transmission of light - and chemistry, which treats of the changes in material bodies arising from alterations in their composition, it must be the case that the early events in the chain leading up to final achievement have occurred at irregular intervals, and often without their influence or possible bearing being realized or even suspected. Many books like this would fail to cover all the details of the complete story; only the briefest summary of the salient points of interest connected with the origins of photographic negative and positive processes will be admissible here.

12. The first definite stage that we note in the unfolding and completion of present-day photography was the invention attributed to the Neapolitan philosopher, Giambattista della Porta, of the "Camera Obscura," This he described in his book on "Natural Magic," published in 1569. He admitted a ray of light through a small aperture in the side of an otherwise darkened room, and found that the image of objects on the outside was thrown on the side of the room opposite the aperture, but reversed - top for bottom and left for right. He also found that a double-convex lens, placed in the aperture, would make the shapes and colors more distinct. This apparatus is the basis of all modern photographic cameras. Instead of the photographer being within the camera, as Porta was, he views the image through a sheet of ground-glass forming one side of it - unless he chooses to dispense with the actual inspection of the image, as he is compelled to by the construction of the majority of hand cameras. With these, a miniature camera, a focusing scale or similar device is employed to secure the focusing and arrangement of the view.

13. Fabricius, in 1556, found that silver chloride, which occurs as an ore, called "Horn Silver," in certain silver mines, turned dark by exposure to light. He prepared the silver chloride artificially, and noted that this compound, white when freshly prepared, likewise turned black by exposure. But he was interested in other matters and made no use of this discovery.

14. Not until 1727 was any application made of this property of darkening in the light which belongs to silver salts in general. In that year Schulze, a German chemist. mixed powdered chalk with silver-nitrate, filled a clear glass bottle with the mixture, and placed on the outside of the bottle a paper label, lettered in black ink. When, after exposure to light, the label was removed, it was found that the parts underneath the ink had been unacted on by light, remaining white, while the translucent paper had allowed the light to pass, and blacken the other parts. Thus the letters appeared in white, on a dark ground; until they too, after the removal of the label, turned dark, like the background. This experiment is the basis of most printing processes involving the use of a negative.

15. Thomas Wedgewood and Humphry Davy, in England, worked along the same lines three-quarters of a century later, the results of their experiments having been published in 1802. They coated white paper or white leather with silver nitrate, and printed thereon, using various opaque objects, also paintings on glass, as negatives. They also experimented with the camera obscura and with the solar microscope - an adaptation of Porta's idea. They were foiled, however, by the low sensitiveness of the silver salt and the impossibility of "preventing the unshaded parts of the delineations from being colored by exposure to the day." In other words they were unable to make their prints permanent - to "fix" them.

16. In experimenting with the then new art of Lithography, Joseph Nicephore Niepce about 1813, tried the substitution of metal plates for lithographic stone and the use of a kind of asphalt as a coating. With the idea of saving labor in drawing, he put the asphaltum-coated plate in the camera-obscura and made a long exposure to a sunlit object. The high-lights acted on the asphaltum, making it insoluble; the shadows had no effect, and permitted the coating to be removed by a solvent. The metal plate, treated with acid, was etched away around the parts that had been protected by the insoluble portions of the coating, and a relief-plate was produced, which could be printed from. Niepce's process, besides giving the suggestion of development of a "latent image," is exactly the same in principle as that now employed in making "half-tone" engraving plates, such as are used in printing the studies and similar illustrations of this book.

17. A prominent scene-painter in Paris, L. J. M. Da-guerre, heard of Niepce's experiments, made his acquaintance, and in 1829 formed a partnership with him for working out the idea into practical form. No particular progress had beeen made when Niepce died, in 1833, and Daguerre continued experimenting along his own lines, finally achieving success in 1838. He announced the full details of this, the first successful photographic process, publicly, on August 19, 1839, and was pensioned by the French government for so doing. Daguerre used a polished plate of silver copper, on which a film or iodide of silver was allowed to form, by exposing the silver surface to the vapor of iodine. This coated plate was then exposed in the camera, and developed by the action of metallic mercury vapor. Fixing was accomplished in a solution of common salt.