Samuel Pierpont Langley
Langley's chief scientific interest was the sun and its effect on the weather, and believed that all life and activity on the Earth were made possible by the sun's radiation. In 1878 he invented the bolometer, a radiant-heat detector that is sensitive to differences in temperature of one hundred-thousandth of a degree Celsius (0.00001 C) . Composed of two thin strips of metal, a Wheatstone bridge, a battery, and a galvanometer (an electrical current measuring device), this instrument enabled him to study solar irradiance (light rays from the sun) far into its infrared region and to measure the intensity of solar radiation at various wavelengths.


Bolometers have been flown on numerous NASA missions including the Earth's Radiation Budget Experiment (ERBE) and the Clouds and Earth's Radiant Energy System (CERES), which provided accurate regional and global measurements of the components of the Earth's radiation budget. Langley's highly original and innovative research earned him honorary doctorates, awards, and medals from universities and scientific societies around the world.

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On the Shoulders of Giants
Samuel Langley
The Bolometer
Links and References

Left: A drawing of a bolometer used by Langley to measure the infrared energy emitted by the sun. (From the Annals of the Astrophysical Observatory of the Smithsonian Institution, Volume I)