Seeing the Unseen 



Looking at Thini^s with Invisible Light 

 By R. W. Wood 



Professor of Experimental Physics, John Hopkins T'niversity 



Professor Wood is one of the most distinguished of American physicists. 

 He has recently attracted attention to himself by ingeniously photographing the 

 common objects around us, as well as the planets, with light that our eyes can 

 never see. Thus he has opened an entirely new tivrld, the exploration of which 

 teems with boundless possibilities. The following article from Professor Wood's 

 pen explains as simply as possible how he conducted his investigation and what 

 may be seen in the strange world that our imperfect eyes can never behold. — -Editor. 



IF you could 

 strike all the 

 keys of a 

 piano at once, 

 from the deep- 

 est base note to 

 the topmost 

 treble, you 

 would create a 

 medley or caco- 

 phony in which 

 it would be im- 

 possible to pick 

 out one sound 

 from another. 

 White light is 

 very much like 

 that. It is a 

 blending of 

 many different 

 kinds of light. 



The analogy 

 between light 

 and sound is 

 closer than may 

 be supposed, if 

 they are re- 

 garded merely 

 as vibrations. 

 The character- 

 istic that dis- 

 tinguishes the 

 lowest base 

 note from the 

 highest treble 

 on a piano is 

 pitch, and pitch 

 depends on freq 

 it is with light, 

 fest themselves 



A photograph taken with ultra-violet light reveals 



no shadows. White objects appear black, and 



everything seems veiled in a thin fog 



uency of vibration. So 

 Low \ibrations mani- 

 as red colors; high 



vibrations as 

 violet hues. 

 Just as there is 

 a perfect musi- 

 cal octave com- 

 prised of notes 

 each having a 

 definite pitch 

 or frequency of 

 vibration, so 

 there is a light 

 scale, manifest- 

 ing itself in 

 color notes, 

 each also hav- 

 ing a definite 

 pitch or fre- 

 quency. But 

 while the fre- 

 quency of the 

 \ibrations that 

 produce musi- 

 cal notes is 

 measured at 

 the most by 

 thousands per 

 -ccontl, the vi- 

 brations that 

 manifest them- 

 selves to our 

 eyes as light 

 must be meas- 

 ured by trillions 

 per second. 



There are 

 sounds so thin 

 and shrill, so 

 highly pitched that only sensitive ears 

 can hear them. Beyond them are notes 

 that no human ear can hear at all. 



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