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Page:Popular Science Monthly Volume 89.djvu/103

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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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