Image: Hertz micrometer resonator

Description: Resonator antenna that German physicist Heinrich Hertz used as a radio wave detector in his first experiments that demonstrated the existence of radio waves. It consists of a helix of brass wire in the shape of a ring, with a spark gap between the ends. It probably functioned as a quarter wave antenna. When the radio waves produced by his spark gap transmitter were at the resonant frequency of the loop of wire, it produced a high voltage between the ends of the wire, which jumped across a tiny spark gap. The spark gap (bottom of loop) was a micrometer with which he could measure the length of the spark, to get an estimate of the field strength of the waves.
Title: Hertz micrometer resonator
Credit: Retrieved December 30, 2014 from Rollo Appleyard, "Pioneers of Electrical Communication 5: Heinrich Rudolf Hertz" in Electrical Communication magazine, International Standard Electric Corp., New York, Vol. 6, No. 2, October 1927, p. 70, fig. 9 on http://www.americanradiohistory.com
Author: Rollo Appleyard
Permission: This 1927 issue of Electrical Communication magazine would have the copyright renewed in 1955. Online page scans of the Catalog of Copyright Entries, published by the US Copyright Office can be found here. Search of the Renewals for Periodicals for 1954, 1955, and 1956 show no renewal entries for Electrical Communication. Therefore the magazine's copyright was not renewed and it is in the public domain.
Usage Terms: Public domain
License: Public domain
Attribution Required?: No