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Page:Popular Science Monthly Volume 89.djvu/106

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��Popular Science MoiifJily

��It is obvious that the world is fully with a horizontal reflecting telescope as well worth studying in light below of fifty-six-foot focus and fourtecn- red (infra-red) as in light above violet. inch aperture to ascertain what might When we reach the infra-red rays we be revealed if the Moon were photo- are dealing with heat rays. A glass lens graphed with ultra-violet light. While will answer our purpose in this case, but there is very little difference between we must use a screen or color filter which ordinary photographs of the lunar sur- absorbs all of the visible and ultra-violet face and those made with ultra-violet

��light, while transmitting the infra-red.

As the cam- era reveals it, the infra-red world is as startling as the ultra-violet world. The sky appears in photographs as black as mid- night ; foliage snow whit e. The shadows are intensely black, simply because most of the light comes directly from the sun and not from the sky.

Applied to purely scientific investigation this utilization of infra-red and u 1 1 r a-v i o 1 e t rays has vast possibilities. I have made photographic studies of the heavenly bod- ies with invisible rays, and the results obtained prove convincingly that many new facts can be reached in this way.

The Moon is a dead, arid, airless body which has long ceased to interest most astronomers. Every one of its many thousand extinct craters has been plotted; its great mountain ranges have all been named; and its so-called "seas" and basins have been mapped. It seemed impossible years ago to add anything substantial to our knowledge of the Moon. I made some experiments at my summer home on Long Island

���Photograph taken with infra-red light. Note

the black sky, the white trees silhouetted

against it, and the deep shadows

��radiation alone, there is enough that is signifi- c a n t. The brightest of all extinct lunar craters is called Aristarchus. Photographed with ultra-vio- let rays, Aris- tarchus shows a dark patch which is not to be seen on a photograph made with vis- ible light. I made an en- largement of the region in which this cra- ter appears, and it is evi- dent that there is in its neigh- borhood a large deposit of some material which can be revealed only by ultra- \' i o 1 e t rays. These photo- graphs of the Moon prove that by systematically stud>ing the lunar surface with invisible rays, we may some day discover what the Moon is made of almost with as much certainty as if we could analyze a piece of it in an earthly laboratory.

In the late autumn of last year, through the courtesy of Professor Hale, the great sixty-inch reflecting telescope of the Mount Wilson Obscrx-atory in California was placed at m\' disjiosal for four nights. The instrument is the largest of its kind in the world. Photo- graphs of Saturn and Jupiter were made

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