Popular Science Monthly 



91 



bromine, contained in a rectangular 

 transparent cell. 



White ink made from Chinese white 

 and written on white paper is practically 

 invisiiilc to our eyes. Photograph it 

 with ultra-violet rays by means of the 

 devices mentioned and it appears on the 

 photograph as if it had been written with 

 the blackest ink. Landscapes photo- 

 graphed by ultra-violet rays reveal no 

 shadows. This means that the molecules 

 of air or the particles of dust in the 

 atmosphere completely scatter the rays, 

 from which it follows that the greater 

 part of the ultra-violet light that reaches 

 the surface of the earth comes from the 

 sky and not directly from the sun. If 

 we saw only with ultra-violet light the 

 world would appear as it does when a 

 thin mist ho\ers over everything. We 

 should, indeed, see the sun, but it would 



It must not be supposed that there is 

 but one ultra-violet light. There are 

 indeed as many colors that we cannot see 

 in the ultra-\iolet region as are visible 

 in the rainbow. Unfortunately the 

 camera and the sensitized plate do not 

 give us true colors, as every kodak 

 user knows; but they do indicate color 

 difTercnces in black and white. The 

 photographs which I have made aiTord 

 convincing evidence that there are a 

 myriad hues in ultra-violet octaves. 

 Thus all white flowers do not appear 

 equally dark on ultra-violet photographs. 

 White geraniums photograph much 

 lighter than common white phlox. 



In the opening paragraphs of this 

 article light and sound were compared. 

 It was stated that just as there are 

 inaudible sounds there are invisible 

 lights. There is a difference, however, 



A check which was "raised" from twenty-four to twenty-four hundred dollars. The upper 



photograph, made with ultra-violet rays, shows the erasure plainly; the lower photograph, 



made by ordinary light, reveals nothing suspicious 



be very dull, and there would be no 

 shadows, just as there are none on a 

 fogg>- day. Garden ilowers which are 

 white in the sun, [)hlox for example, 

 become almost black. Who knows 

 but this ability of white flowers to 

 absorb ultra-violet rays may play some 

 economic part in the growth in the 

 plant? I made some experiments to 

 answer that question, but without 

 success. But who knows what the 

 result would be after several generations 

 of plants had been grown without the 

 influence of ultra-\iol(t light? 



bet^veen the sound ra>s and light rays. 

 As you go below the scale of musical 

 notes, as you lower the number of 

 \ibrations, you hear not musical notes 

 but distinct beats or blows. That 

 happens when there are less than sixteen 

 vibrations in a second. But — you hear. 

 As you go down the light scale beyond 

 red, the vibrations decrease in number 

 by millions in a second. But — you do 

 not sec. In other words there is but 

 one small octave of visible light. Above 

 and below that octave we see nothing 

 with our eves. 



