PHYSICAL RESEARCHES CONTINUED 81
mere spoiling by climate. But, as Bose's theory explains, he now saw it as a recovery of the plates from their image-strained condition. For some time later, wishing urgently to take a photograph, at a moment when he had not a single fresh plate available, it occurred to him, as a mere chance, to try one of those spoiled Indian plates, of which the development had been abandoned. To his agreeable surprise the new photograph was successful—in fact, as if the plate had been a fresh one. He now for the first time understood, and brought his experience forward as a vivid confirmation of Bose's theory of strain and recovery.
Substances may be sensitive, yet give no photographic image. For on the same general view, since almost all substances are molecularly affected by radiation, though in different degrees, and with very different rates of recovery, it is theoretically possible that we may alike vary the sensitive material for our photographic images, and find a widening range of developers for them. And in the world of nature our conception of activities of radiant energies through the whole spectrum, and of their effects upon recipient matter, similarly expand thereby. And if this is true throughout the range of inorganic matter, why should it not hold good in the living world as well, sensitive to radiation as we know it to be? Here, however, we are somewhat outrunning the paper before us, though not its author's active mind.
As examples of sensitive substances other than photographic plates with their salts of silver, why not plates of other materials? Moser had already obtained invisible images by prolonged exposure of clean silver and copper plates, which he developed with mercury vapour; and Waterhouse had made similar experiments, even with lead and gold, using the common developers. Since Bose had found all metals sensitive to electric radiation, the sensitiveness to light also was what he expected, while the prolonged exposure found necessary was to provide the
