Thomas Edison invented the tasimeter to detect extremely small changes in temperature, including those caused by starlight.
Edison developed the instrument in 1878 while exploring ways to measure heat radiation. The tasimeter used a sensitive strip of carbon whose electrical resistance changed when the material expanded or contracted. That change could be detected electrically, allowing the device to register very small temperature variations.
Edison hoped the instrument could help astronomers study the heat emitted by celestial bodies. He took a tasimeter to Wyoming for observations of a total solar eclipse on July 29, 1878, expecting it might detect heat from the solar corona. The results were not as decisive as he hoped, but the instrument became an example of Edison’s work outside his best-known electrical and recording inventions.
The tasimeter is often confused with a thermopile, which also measures radiant heat but uses electrical effects produced at junctions of different metals or semiconductors.