. Annual report of the Board of Regents of the Smithsonian Institution. Smithsonian Institution; Smithsonian Institution. Archives; Discoveries in science. 68 ANNUAL EEPOET SMITHSONIAN INSTITUTION, 1911. much less for violet and ultra-violet rays than for red and infra-red ones, we probably get infra-red rays from deeper-lying and hence hotter layers in the sun than we do ultra-violet ones. We conclude that the solar radiation comes from sources ranging in tem- perature perhaps between the limits 5,000° and 7,000° absolute centigrade, but mostly from sources between 6,000° and 7,000°. Washingt
. Annual report of the Board of Regents of the Smithsonian Institution. Smithsonian Institution; Smithsonian Institution. Archives; Discoveries in science. 68 ANNUAL EEPOET SMITHSONIAN INSTITUTION, 1911. much less for violet and ultra-violet rays than for red and infra-red ones, we probably get infra-red rays from deeper-lying and hence hotter layers in the sun than we do ultra-violet ones. We conclude that the solar radiation comes from sources ranging in tem- perature perhaps between the limits 5,000° and 7,000° absolute centigrade, but mostly from sources between 6,000° and 7,000°. Washington observations.—Further experiments have been made, under Mr. Fowle's direction, on the transmission of radiation of great wavg lengths through long columns of air containing known qualities of water vapor. Many of these observations are not yet reduced, go that it is not yet proper to give a numerical summary of results. The length of the column experimented upon has been increased to 800 feet. The measurements cover the infra-red spectrum, from the A line to a wave length of about 17^4. The observations of the water contents of the air column are made by means of pairs of wet and dry therinome- ters located at a number of points along the path. The air is thoroughly stirred before readings. Check experijuents by Mr. Aldrich, in which he drew the air through phosphorus i^entoxide tubes and weighed the water absorbed, have conOrmed the accuracy of the water-vapor determina- tions. Mr. Fowle has made a preUminarj- comparison of the upper infra-red spec- trum bands p, <j, t, ^, <ij, and as observed through the tube with ihe same bands as observed through the whole atmosphere at Washington, Mount Wilson, and Mount Whitney. The re- sults are most interesting, though not yet ripe for publication, and will probably lead to more exact knowledge of the total quantity of water vapor in the atmos- phere, and its variation with the altitude of the observer and the season
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