History Coherer

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branly s electrical circuit tube filled iron filings (later called coherer )


in 1890, french physicist edouard branly published on changes in resistance of bodies under different electrical conditions in french journal described thorough investigation of effect of minute electrical charges on metal , many types of metal filings. in 1 type of circuit, filings placed in tube of glass or ebonite, held between 2 metal plates. when electric discharge produced in neighbourhood of circuit, large deviation seen on attached galvanometer needle. noted filings in tube react electric discharge when tube placed in room 20 yards away. branly went on devise many types of these devices based on imperfect metal contacts. branly s filings tube came light in 1892 in great britain when described dr. dawson turner @ meeting of british association in edinburgh. scottish electrical engineer , astronomer george forbes suggested branly s filings tube might reacting in presence of hertzian waves, type of air-borne electromagnetic radiation proven exist german physicist heinrich hertz (later called radio waves).



marconi s 1896 coherer receiver, @ oxford museum of history of science, uk. coherer on right, decoherer mechanism behind it. relay in cylindrical metal container (center) shield coherer rf noise contacts.


in 1893 physicist w.b. croft exhibited branly s experiments @ meeting of physical society in london. unclear croft , others whether filings in branly tube reacting sparks or light sparks. george minchin noticed branly tube might reacting hertzian waves same way solar cell did , wrote paper action of electromagnetic radiation on films containing metallic powders . these papers read english physicist oliver lodge saw way build improved hertzian wave detector. on 1 june 1894, few months after death of heinrich hertz, oliver lodge delivered memorial lecture on hertz demonstrated properties of hertzian waves (radio), including transmitting them on short distance, using improved version of branly s filings tube, lodge had named coherer , detector. in may 1895, after reading lodge s demonstrations, russian physicist alexander popov built hertzian wave (radio wave) based lightning detector using coherer. same year, italian inventor guglielmo marconi demonstrated wireless telegraphy system using hertzian waves (radio), based on coherer.


the coherer replaced in receivers simpler , more sensitive electrolytic , crystal detectors around 1907, , became obsolete.


one minor use of coherer in modern times japanese tin-plate toy manufacturer matsudaya toy co. beginning 1957 used spark-gap transmitter , coherer-based receiver in range of radio-controlled (rc) toys, called radicon (abbreviation radio-controlled) toys. several different types using same rc system commercially sold, including radicon boat (very rare), radicon oldsmobile car (rare) , radicon bus (the popular).








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