. Annual report of the Board of Regents of the Smithsonian Institution. Smithsonian Institution; Smithsonian Institution. Archives; Discoveries in science. 158 SOME EECENT ASTKONOMICAL EVENTS. Notwithstanding this discouraging evidence, the question was again taken up within the last two or three years by Professor Nichols with his radiometer. Before mentioning his results it will be of interest to lirietiy describe that instrument. The principle upon which it is based is the well-known one of the Crookes revolving vanes, familiar in the collections of appa- ratus exhibited in the physical cab
. Annual report of the Board of Regents of the Smithsonian Institution. Smithsonian Institution; Smithsonian Institution. Archives; Discoveries in science. 158 SOME EECENT ASTKONOMICAL EVENTS. Notwithstanding this discouraging evidence, the question was again taken up within the last two or three years by Professor Nichols with his radiometer. Before mentioning his results it will be of interest to lirietiy describe that instrument. The principle upon which it is based is the well-known one of the Crookes revolving vanes, familiar in the collections of appa- ratus exhibited in the physical cabinets of academies and colleges. In this interest- ing toy a pair of small metallic vanes, blackened on opposite sides and fixed perpendicularly upon a light arm, itself horizontal and delicately poised at its center upon a vertical axis, is caused to rotate in a vacuum by the influence of light. The Nichols radiometer is merely this instrument adapted to measure the intensity of the impinging rays. An idea. ^^ #--® , m m fe The Nichols radiometer. From Astrophysical Journal, Vol. xiii, No. 2, March, 1901. of its construction is given by the accompanying diagram. The vanes, made very small, are fastened at the ends of a slight stem of glass about one-fourth of an inch long, which in turn is fixed at right angles to a second longer glass stem furnished with a very light mirror and sus-. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Smithsonian Institution. Board of Regents; United States National Museum. Report of the U. S. National Museum; Smithsonian Institution. Report of the Secretary. Washington : Smithsonian Institution
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