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 (pl. 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. 
Tn 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 amagazine. In the photograph (pl. 4, fig. 2) taken with 
visible light 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 ight 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 
