Aspects of this topic are discussed in the following places at Britannica.
...Alexandre-Edmond Becquerel reported that only a few volts were required to drive electric current through the air between high-temperature platinum electrodes. From 1882 to 1889, Julius Elster and Hans Geitel of Germany developed a sealed device containing two electrodes, one of which could be heated while the other one was cooled. They discovered that, at fairly low temperatures, electric...
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