File:Hughes carbon microphone.jpg

No higher resolution available.

Hughes_carbon_microphone.jpg (217 × 346 pixels, file size: 26 KB, MIME type: image/jpeg)

This is a file from the Wikimedia Commons. Information from its description page there is shown below.
Commons is a freely licensed media file repository. You can help.

Summary

DescriptionHughes carbon microphone.jpg	English: Crude carbon microphone invented by David Edward Hughes in 1878. It consists of a carbon rod suspended by its pointed ends vertically between two metal electrodes. Sound vibrations transmitted from the wooden back to the carbon-steel contact causes varying pressure on the carbon granules, causing variation in the carbon's resistance. Edwards found that the device was very sensitive, he was able hear the sound of a fly walking on it, and named it "microphone". Edwards did not invent the microphone but experimented with a wide range of "microphonic" electrical contacts.
Date	January 1932
Source	Retrieved October 27, 2015 from Thomas Elway, "The Microphone - Radio's electric ear" in Radio News magazine, Teck Publishing Co., Dunellen, New Jersey, Vol. 8, No. 7, January 1932, p. 557 on http://www.americanradiohistory.com website
Author	Thomas Elway
Permission (Reusing this file)	This 1932 issue of Radio News magazine would have the copyright renewed in 1960. 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 1959, 1960 and 1961 show no renewal entries for Radio News. Therefore the magazine's copyright was not renewed and it is in the public domain.

Licensing

This work is in the public domain because it was published in the United States between 1929 and 1963, and although there may or may not have been a copyright notice, the copyright was not renewed. For further explanation, see Commons:Hirtle chart and the copyright renewal logs.
Note that it may still be copyrighted in jurisdictions that do not apply the rule of the shorter term for US works (depending on the date of the author's death), such as Canada (70 years p.m.a.), Mainland China (50 years p.m.a., not Hong Kong or Macao), Germany (70 years p.m.a.), Mexico (100 years p.m.a.), Switzerland (70 years p.m.a.), and other countries with individual treaties.

العربية ∙ Deutsch ∙ English ∙ español ∙ français ∙ galego ∙ italiano ∙ 日本語 ∙ 한국어 ∙ македонски ∙ português ∙ português do Brasil ∙ русский ∙ sicilianu ∙ slovenščina ∙ українська ∙ 简体中文 ∙ 繁體中文 ∙ +/−