During the ten years from 1876 to 1886 photography underwent a complete revolution owing to the introduction of the gelatino-bromide plate and as this new phase gave us a great deal to think about, and a great deal of new experience to acquire, our work during these ten years was not wholly confined to what he has previously indicated, but had been directed towards discovering some method of testing the speed of plates, which was workable in the laboratory and independent altogether of the camera.
The production of a photograph is governed by natural laws, and a definite effect must result from a definite cause. The same cause, under the same conditions, always produces the same effect. The law which governs the action of light upon the sensitive plate teaches us that only a limited range of such action is available in photography if truthful representation be demanded, and hence the necessity of accuracy in exposure...
I earnestly hope that this little work may be the means of inducing some amateur photographers to take up the scientific method, and I feel very confident in assuring any who may do so that they will discover a new field of unexpected pleasure in the pursuit of photography.
The fluctuations of light throughout the year and again throughout the day, are so great that no photographer could adequately allow for them with any certainty of a proper exposure. The best he could do was to make a more or less well-founded guess. It was clear that such a matter must be governed by a law of nature and with the object in view, therefore, of reducing exposure to a system we made up our minds to work together at the subject.
One of the greatest difficulties the photographer, and especially the amateur has to encounter, lies in correctly estimating his exposure. Of course, by one who is in the habit of making almost daily exposures, experience is gained, which is a more or less certain guide, but by the photographer, who only occasionally exposes a plate, some better guide is required if certainty of result is to be expected. The fluctuations of the light throughout the year, and again throughout the day, are so great that we believe nobody, be he professional or amateur, can adequately allow for them unless he has some reliable data to go upon. Then, again, with the era of gelatino-bromide dry plates, a new difficulty arose in consequence of the great variety in their speeds. This is a very serious complication, and has never hitherto been scientifically dealt with, a satisfactory unit of speed never having been found.
Further, we had long felt that art in photography ceased to play any part the moment the cap was removed from the lens, and that very subsequent operation, whether exposure, development, printing or enlarging, was strictly a matter of science, and amenable to calculation. While we quite realized that the artist will always produce the best picture, we contended that the scientist will produce the best negative. The photographer, therefore, who combines scientific method with artistic skill is in the best possible position to produce good work. Hence, our aim was to raise technical photography from an empirical art to a quantitative science.