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−1 and about three times greater at 100 cm−1. Between 20 and 50 cm−1 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−1 in layers of 0.6-mm thickness and then increased rapidly in transmittance. A narrow absorption band is present at 112 cm−1 and causes the rapid increase in transmittance on its low-frequency side. Other materials measured only increased appreciably in transmittance over wide regions of the spectrum.
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