The Cine Technician (1939)

44 THE (IN E-TEC HNICI AN June-July, 1937 to the rubbish heap, but being made of silver it was naturally laid aside in a cupboard to be repolished and again prepared a ir a fresh exposure. "How rnanv of us would have lost heart at this point and abandoned the whole affair as a practical impossibility ? Not so with the indefatigable Daguerre. It was no light task to repolish the silver plate ; it requires great skill and care. I fancy that Daguerre must have come forward to open his cupboard next morning with a feeling of dogged perseverance ; nothing for it but to try, try, try again. Imagine his surprise when he took the spoilt plate from the cupboard to find an exquisite picture upon it. Doubtless he questioned whether he was waking or dreaming ; it was too like a fairy tale. A perfect picture ! Nothing approaching it lias ever been seen by man before. "Wherein could lie the magic power of his cupboard ? Will another short exposure in the camera — another 24 hours' imprisonment in the cupboard-present him with another 'perfect picture' ? I very much doubt if Daguerre slept the following night. At any rate there would be no chance of his sleeping on and failing to remove the second plate on the expiring of the twenty-four hours. "Another picture did appear, and equal in every way to the first, ami so it only remained for Daguerre to discover wherein lay the magic in his cupboard. "It was clear that the plate must have been affected by vapours from some of the chemicals in the cupboard, and so a little patience would be required to find out which dish of chemicals was the 'good fairy.' I think that the one which did prove itself to be the magical one was one of the last that Daguerre would have suggested. It was a simple dish of that bright semi-liquid metal known as mercury. In this way Daguerre discovered that if what he had previously considered to be a very much under Fio. 1. Fig, 3. Diagrams showing^working of William FrieseGreene's first motion picture camera. WILLIAM FRIESE-GREEN. exposed plate was exposed to the vapour of mercury, the invisible image was gradually built up into a visible picture. "What really happened was that the mercury vapour attached itself to the sensitive plate in exact proportion to the amount of light which had previously affected the plate while in the camera. "Here we have the sensitive plate receiving a latent image, which only appears when chemically developed. To the photography of to-day^ this has ceased to be a marvel, but to Daguerre and his compatriots it was indeed a true romance." Daguerre had previously succeeded in making his pictures permanent by fixing them, washing them in a solution of common salt. By this means the remaining iodide of silver which had been unaffected bv the light was washed away, so that there could be no further chemical action. Sir John Herschel, the famous astronomer, suggested later that hyposulphate of soda was a better substance than common salt (chloride of soda) wherewith to fix the image. This hypo-fixer is, of course, still supreme to-day. At the same time when Daguerre was experimenting in France, William Henry Fox Talbot, in England, was also hard at work more or less on the same lines as Daguerre, and there seems no doubt that it was only because Daguerre announced his invention to the world first, that the official dates of this phase of photography are credited to Daguerre. Nevertheless, Talbot was in some sense ahead of Daguerre, because he was making prints from his negative papers. He apparently went through the same trials as Daguerre, starting off with silver nitrate and common salt, making .1 solution of chloride of silver. He also tried iodine to form iodide of silver, but it was not until he discovered the use ol gallic acid in development, that he improved his pictures considerably in detail and found that his exposure m the camera could be much shorter. (John Frederick Goddard discovered that a vapour of bromine, a non-metallic element, greatly increased the speed oi exposure used in conjunction with Daguerreotype plates, and he was able to make an exposure in 20 seconds iusie.nl oi .1 m.m\ minutes). Fox Talbot was therefore able to develop the latent image which was called the negative. (Sir John