The radiant energy from a quartz mercury lamp has been compared with the energy from a globar source. It was found that the energy of the mercury lamp was about six times greater at 50 cm<sup>-1</sup> and about three times greater at 100 cm<sup>-1</sup>. Between 20 and 50 cm<sup>-1</sup> very little energy is emitted by the globar. The measurements were made on a Michelson type interferometer operating under the same conditions for each source. Several materials were measured in a search for filters for the far-infrared region. Magnesium oxide was found to be opaque to 110 cm<sup>-1</sup> in layers of 0.6-mm thickness and then increased rapidly in transmittance. A narrow absorption band is present at 112 cm<sup>-1</sup> and causes the rapid increase in transmittance on its lowfrequency side. Other materials measured only increased appreciably in transmittance over wide regions of the spectrum.
EARLE K. PLYLER, D. J. C. YATES, and H. A. GEBBIE, "Radiant Energy from Sources in the Far Infrared," J. Opt. Soc. Am. 52, 859-861 (1962)