from The Century Dictionary and Cyclopedia
- n. A spectrum of a thermal radiation, considered not with reference to its effect upon the eye, but with reference to its intrinsic energy or heating power.
Sorry, no etymologies found.
For in February, 1885, Professor Langley succeeded, after many fruitless attempts, in getting measures of a "lunar heat-spectrum."
1886 Solar heat-spectrum extended by Langley to below five microns.
1885, February Langley measures the lunar heat-spectrum.