“Perhaps the best known instrument for measuring solar heat is one which ought to be considered, among those still in use, the worst in principle, and in practice one of the most untrustworthy. I refer to the pyrheliometer of Pouillet, which was the best attainable fifty years ago, and which is to be found described in every text-book on the subject.” So wrote Samuel Pierpont Langley, the director of the Allegheny Observatory, in his account of his 1881 expedition to Mount Whitney, to measuring solar radiation with his newly developed bolometer.
Charles Greeley Abbot, Langley’s assistant and then successor at the Smithsonian Astrophysical Observatory, apparently thought more highly of pyrheliometers. This example came from the S.A.O., and may have been made by Abbot, or under his direction.
Ref: S. P. Langley, Researches on Solar Heat (Washington, D.C., 1884), p. 51.
C. G. Abbot, “The Silver Disk Pyrheliometer,” Smithsonian Miscellaneous Collections (Washington, D.C., 1911).
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