EXPERIMENTS WITH INVISIBLE LIGHT WOOD. 161 



hand, are completely scattered, so that the greater part of the ultra- 

 violet light which reaches the surface of the earth comes from the sky 

 and not directly from the sun. If our eyes were sensitive only to 

 ultra-violet we should find the world appearing not greatly different 

 from the aspect which obtains at the time of light fog. We should, 

 indeed, see the sun, but it would be very dull, and there would be no 

 shadows, just as there are none on a foggy day. We should walk the 

 earth like Peter Schlemeil, the shadowless man of the German fable. 



The next picture (pi. 3, fig. 2) illustrates the opacity of ordinary 

 window glass to ultra-violet radiation. It will be noticed that there 

 is no trace of the landscape seen through the glass window, although 

 it is clearly rendered in the companion picture taken with visible light. 

 Another difference to be noted in these pictures is that the flowers in 

 the garden, which are white in the picture taken with visible light, 

 disappear entirely in the picture taken by means of the ultra-violet 

 radiation. The white garden flowers become almost black, as is 

 shown in plate-4, figure 1, which shows white phlox photographed by 

 visible and ultra-violet light. It occurred to me that this ability of 

 the white flowers to absorb the ultra-violet rays might play some 

 economic part in the growth of the plant. I therefore experimented 

 with some flowers which had been grown under glass, and had thus 

 been deprived of ultra-violet, but I was unable to find any marked 

 difference between those which had been grown in the open and 

 others which had been deprived of their full quota of this radiation. 

 It is possible that if the experiments were carried on through the 

 course of a number of generations, we should find a difference. I 

 have found, however, that all white flowers are not equally dark when 

 photographed with ultra-violet light. White geraniums, for example, 

 come out much lighter than common white phlox, which is practically 

 black when photographed through the silvered quartz lens. 



In order to demonstrate the difference in the appearance of one of 

 the common pigments when viewed respectively with visible light and 

 with ultra-violet radiation, some letters were painted in Chinese white 

 on a page of a magazine. In the photograph (pi. 4, fig. 2) taken with 

 visible fight the Chinese white appears as white as the paper itself, if 

 not indeed whiter; but, photographed with the ultra-violet radiation, 

 it comes out absolutely black. One may say that what is Chinese 

 white in visible light becomes Japan black in ultra-violet. Under 

 this radiation also black printer's ink becomes lighter than in visible 

 light. This failure in the reflecting capacity of Chinese white is a 

 source of some annoyance in reproducing drawings executed in part 

 in this medium, as has been pointed out by Mr. A. J. Newton. In 

 working with my Chinese white I made a mistake in one letter in the 

 word " appears," and carefully wiped it out, leaving no trace of the 

 38734°— sm 1911 11 



