Bolometer, an instrument used to measure infrared, or heat, radiation. The bolometer is essentially a very sensitive thermometer. It can be used with a spectroscope to measure the ability of certain chemical compounds to absorb various wavelengths of infrared radiation. These measurements provide valuable information about the structures of these compounds. The bolometer has also been used to measure the temperature of the moon's surface through a telescope.

A bolometer contains a thin, blackened strip of platinum metal. Heat radiation falling on the strip changes its resistance to an electric current. This change is recorded by a sensitive electric meter. The instrument was invented in 1878 by Samuel P. Langley.