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 photo- 

 graphic 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 



