pyroheliometer

Updated: May 9, 2025

He then refers to the actinometer and pyroheliometer, instruments for measuring the actual heat derived from the sun, and also to the Bolometer, an instrument invented by Professor Langley for measuring the invisible heat rays, which he has proved to extend to more than three times the length of the whole heat-spectrum as previously known, and has also shown that the invisible rays contribute 68 per cent, of the sun's total energy.

Alfred Russel Wallace - Is Mars habitable? A critical examination of Professor Percival Lowell's book "Mars and its canals," with an alternative explanation