PHYSICAL RESEARCHES CONTINUED 85 



in fact of its ' Natural Magic/ as the old physicist Porta 

 called his book, still memorable for his description of the 

 ' Camera Obscura/ which is now reduced in size into the 

 photographic camera. The camera is indeed a sort of 

 giant eye ; and its sensitive plates are a kind of simple 

 and inorganic retina. Correspondingly, the eye is a camera, 

 and its / retina an organically elaborated sensitive plate, 

 subtly layered for the perception of different shades of light. 

 This further invention of Bose's incredible or un- 

 canny though to some it seemed at first comes into line 

 with our general and elementary understanding of eye 

 and camera alike : the wonder is in its immense range 

 of sensitiveness. Yet instead of finding any super-retinal 

 elaboration, well-nigh beyond microscopic inquiry, still 

 more beyond mere dissection, when we open the little globe 

 of the electric eye, and take away its lens, this amazing 

 super-retina turns out to be made but of two tiny crystals 

 of galena, adjusted to contact-sensitiveness. That this 

 common lead ore, this heavy sulphide, should of all known 

 things have fullest sensitiveness to all ether-waves, of nature 

 or of laboratory art, is worth reflecting on. Lead ' dull 

 lead ' is less dull than we think ! And the characteristic 

 response of the artificial retina next led Bose to discover, 

 as we shall see later, certain unsuspected phenomena in 

 human vision. 



