18. The pictures produced by this process, called, in honor of the inventor, "Daguerreotype," have never been surpassed in delicacy and beauty. They are not really positives, but negatives of exceeding thinness, "backed" by the mirror-like surface of the silver. This is the reason why the earliest daguerreotype pictures are reversed. Thus, in a portrait, if the right hand rested on a table, the daguerreotype would show it as the left. This drawback was overcome by interposing a mirror or a reflecting prism. But the greatest inconvenience, and one impossible to overcome, was this, that only one plate could be made for each operation; every duplicate required a separate operation.

19. While Daguerre was experimenting in France, another investigator was at work in England, along quite different lines - those of Schulze and Wedgewood and Davy. William Henry Fox-Talbot announced his process in January, 1839, subsequent to the announcements of Daguerre's discovery, though previous to his public divulging of its details.

20. Talbot in his original process used paper coated with silver nitrate and chloride in combination, making prints of opaque objects, as Wedgewood and Davy had done, but fixing them with a solution of common salt. He also discovered that this paper, exposed in the camera for a much shorter time than was needed to produce a visible image, received an impression, a latent image, which could be developed by a solution of nut-galls; and that this image, which was reversed, not only in regard to position, but also to lights and darks, could be used as a negative, from which to produce, by contact, positives, to any required extent. To this process he gave the name "Calotype," and is entitled to the credit of originating, in principle, the method now universal.

21. To John Herschell is due the use of the compound usually termed "Hypo" - really Sodium Thiosulphate - as a fixing agent. This was adopted in practice and its introduction marks an important epoch. Although glass plates had been used incidentally by Wedgewood and others in photographic experiments, the suggestion of their use, instead of paper, in producing negatives, seems to have been Herschell's also. The very important "Blueprint" or Ferro-prussiate process, so extensively utilized in modern industrial and engineering work is another of his contributions to photographic progress.

22. The discovery of gun-cotton, in 1846, by Schonbein, was destined to have an important effect on photographic methods, a few years later. Ordinary cotton fibre, treated with "Aqua Regia," a combination of nitric and hydrochloric acids, is so altered in composition as to become soluble. It is interesting to note, in passing, that gun-cotton enters also into the composition of celluloid, the basis of "films."

23. Niepce de St. Victor, a nephew of the original Niepce, using glass plates for the negative support, made them practicable by employing starch and albumen as a medium which adhered closely to the glass surface, while carrying an iodide in combination. This coating was sensitized by application of silver nitrate; development with gallic acid and fixing with potassium bromide completed the process.

24. Blanquart-Everard, in 1848, applied the albumen coating to paper for printing. The albumen acts as a "size" and results in keeping the chemicals and consequently the image, on the surface of the paper, instead of sinking into its substance. The usefulness of "Albumenized paper" for print making secured the wide adoption of this process, the earliest of the "glossy" as distinguished from the "matt" class of printing papers. In 1850 Gustav Le Gray, although not the originator of collodion, used it to replace albumen as a coating and medium. Collodion, the solution of gun-cotton in mixed ethyl-ether and alcohol, leaves a fine transparent coating of film on a glass plate on which it has been poured, the ether-alcohol solvent quickly evaporating.

25. These experimental suggestions and partial successes were combined, in 1851, by Frederick Scott Archer, into practical working shape, as the "Wet Collodion" process. So effective and satisfactory was it that it was everywhere adopted, supplanting Calotype, Daguerreotype and all other "types" for practical purposes and keeping the field almost entirely to itself until about 1880. Its drawback was the condition that the plates must be sensitized by immersion in a nitrate of silver bath and used almost immediately. Whenever exposures were to be made at any distance from studio or work-room, this imposed the necessity of transporting a cumbrous outfit for sensitizing and development in a portable dark-room of some sort. The results, under proper conditions, have, however, never been surpassed by any other process in the prompt and sure production of negatives having perfect transparency in the darks and opacity in the high-lights, together with satisfactory gradation in the intervening "half-tones." The "contrasty" properties of such negatives render them still the mainstay of the photo-engraver today.

26. In 1855 Taupenot suggested the "dry-plate bath" process. He employed "preservatives" - gallic acid, honey and albumen - to prevent the crystallization of the silver nitrate which occurs when a sensitized wet-collodion plate is allowed to dry. This crystallization renders the action of exposure and development uneven, spoiling the result. Other experimenters, at about the same time, employed tannin, sugar, beer, gum, resin, tea, coffee and tobacco and many other substances, as preservatives; but none of the methods became widely popular, although special workers produced notably successful results in numerous instances.

27. In 1864, Sayce and Bolton published the details of a collodion-emulsion. The principle of this process was the use of the sensitizing agent, the nitrate or other salt of silver, in practically the precise quantity required for the chemical combination that occurred, through the action of light, on exposure. Up to this time it had been the practice to have the silver nitrate in excess. The collodion emulsion could be prepared in bulk and used at convenience for coating glass plates, which were dried and could then be used as required. Many workers contributed to the perfecting of the details of this process, but all their results were superseded by the next advance, the Gelatin-Bromide process.

28. In 1871, Dr. Maddox suggested and worked out the idea of substituting a solution of gelatin in water for the solution of collodion in spirits, combining it with bromide of silver. This suggestion was eagerly taken up by the experimenters and within the next decade the commercial production of gelatin dry-plates on a large scale had become a reality, and the actual popularization of photography, rendering it available to all, had begun.

29. From 1880 to the present time, modifications and improvements, optical, mechanical and chemical, have followed in such bewildering profusion that it is impossible to summarize them, even briefly. They have resulted, on the negative-making side, in wonderfully increased sensitiveness, reducing the necessary time for exposures so that thousandths of a second have become among the commonplace. Where time is not the chief object, then other results, such as color sensitiveness, are attained. Most recent are the wondrous results obtained by the Lumiere color process, attained along new lines of application, and promising far greater advances for the future.

30. Mechanically, the invention of an American, Dr. Goodwin, which substituted for fragile, heavy, rigid glass a support of celluloid, a substance at once flexible, light and tough and practically of equal transparency, has really revolutionized photography on its practical side and rendered it popular to an extent difficult to realize.

31. The practical introduction of this improvement and the countless accessory apparatus, cameras and the like, is to be credited to another American, George Eastman, who has made "Kodak" a household word throughout the world. Indeed, to many thousands of people it involves and comprehends the entire meaning of "Photography." The nature of the material permits of its manufacture in rolls of any desired length, available for one, a half-dozen, or a thousand exposures. By the ingenious application of well known principles, these rolls in the shape of "cartridges" may be put into and removed from suitable cameras in full daylight, without injury to the result.

32. A still more striking instance of the adaptability of such rolls is their use, in quantities measurable only by thousands of miles, for making the negatives and positives employed in one of the latest applications of photography, the Cinematographs or "moving pictures." This use bids fair to overshadow, by comparison, the quantities, already so large, of material required in other photographic fields. And now that cinematographic pictures, closely approximating "natural colors," have been announced as an accomplished fact, the mind can scarcely comprehend what further increase this will involve.

33. It cannot be amiss to call the attention of those who may read the foregoing brief survey of the origins and progress of photography to the importance of an acquaintance with its historical side. Not a week passes that does not see some new use or application made of methods that are, by comparison, old; and to those who are ambitious of advancing, as students and practitioners, nothing can be more useful than an acquaintance with what has been done by their predecessors in the field, to whose devoted labors the present day owes its debt for the knowledge it has received from them.