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Page:Popular Science Monthly Volume 89.djvu/105

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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.

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