They used a thermopile to determine that sunspots were cooler than the surrounding regions.
From the en.wikipedia.org
His measuring device, which used thermopile technology, is an early landmark in the history of absorption spectroscopy of gases.
From the en.wikipedia.org
All measurements were performed using a continuously thermopile-calibrated solar simulator with neutral density filters as described in detail by Ito et al.
From the nature.com
Thermocouples in series form a thermopile, sometimes constructed in order to increase the output voltage, since the voltage induced over each individual couple is small.
From the en.wikipedia.org
Melloni's reputation as a physicist rests principally on his discoveries in radiant heat, made with the aid of the thermomultiplier, a combination of thermopile and galvanometer.
From the en.wikipedia.org
In developing the capability for terahertz laser radiometry, NIST is building a terahertz laser designed for routine measurements and a detector called a thermopile to measure the laser's power.
From the sciencedaily.com
More examples
A kind of thermometer for measuring heat radiation; consists of several thermocouple junctions in series
A thermopile is an electronic device that converts thermal energy into electrical energy. It is composed of thermocouples connected usually in series or less commonly in parallel. ...
Apparatus that consists of a number of thermocouples combined so as to multiply the effect and is used for generating electrical current.
A large number of thermocouples connected in series.
An arrange of multiple thermocouples in series such that the thermoelectric output is amplified.
Measures thermal radiation by absorption to become hotter than its surroundings. It is a number of small thermocouples arranged like the spokes of a wheel with the hot junction at the hub. ...
An array of usually series connected thermocouples designed to increase to signal level and or provide a degree of spatial temperature averaging.