Geitel, Hans

German physicists Julius Elster and Hans F. Geitel invent the first photoelectric cell as a result of studying the photoelectric effect. The first hydroelectric generator at Niagara Falls, New York, produces alternating current from a Nikola Tesla design. 

After Julius Elster and Hans Geitel had noticed that the electrical conductivity of the air in caves and closed cellars is higher than that in the free atmosphere, they finally found that this was caused by the presence of emanations, or radioactive gases, in the ground. In a series of investigations from 1901 to 1906 they demonstrated the presence of radioactive elements in various kinds of rocks and soils, and showed that minute amounts of both radium and thorium are widely distributed in the earth s crust, in spring waters, in sea water, and in the atmosphere (85, 96). 

July 16, 1915) Karl Bergwttz, Julius Elsters und Hans Geitels Bedeutung fur die atmospharische Elektrizitat, ibid., 3, 377-83 (July 16, 1915). 

Elster-Geitel Festchr. Arlwiten aus den Gebieten der Physik, Mathematik, Chemie, Festschrift Julius Elster und Hans Geitel, Brunswick, 1915. 

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