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ASTRONOMY: R. W. WOOD
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MONOCHROMATIC PHOTOGRAPHY OF JUPITER AND SATURN By R. W. Wood DEPARTMENT OF PHYSICS, JOHNJS HOPKINS UNIVERSITY Received by the Academy. January 28, 1916
Photographs of the moon, which I made several years ago by means of ultra-violet light, revealed the existence of an extensive dark area surrounding the crater Aristarchus, which did not appear on plates made by means of yellow light, and could not be detected visually. Control experiments, made in the laboratory, made it appear probable that this deposit consisted of sulphur or sulphur bearing rock. It appeared to me probable that even more interesting results would be obtained in the case of the planets, especially Mars, and preliminary experiments were carried on during the past summer at my East Hampton Laboratory with a horizontal telescope of 56 feet focal length and 16 inches aperture, figured by Mellish, and nickel plated by the method described in the Astrophysical Journal for October. A deposit of nickel is necessary for the reason that silver reflects only 4% of the light in the region of the spectrum utilized, which lies between wave-lengths 3000 and 3300. This mirror was utilized in conjunction with a large Gaertner coelostat, which was placed at my disposal by the Naval Observatory. The mirror of this instrument was replaced by a 16-inch flat, also nickel plated, and photographs were made of the moon and Jupiter by means of infra-red, yellow, violet and ultra-violet light. Notwithstanding the fact that a moving plate holder, provided with eye-pieces for accurate following, was used, it was found difficult to secure sufficiently sharp definition, owing to the rather rapid periodic drift of the image which was very difficult to follow. The seeing moreover was not very good, and on the few nights when it was fair the mosquitoes were bad. Much valuable experience was gained however in