Lee de Forest | American Inventor & Radio Pioneer

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class="md-content"> <div class="md-article-container template-desktop"> <div class="infinite-scroll-container article last"> <article class="article-content container-lg qa-content px-0 pt-0 pb-40 py-lg-20 content md-expanded" data-topic-id="153484"> <div class="grid gx-0"> <div class="col-auto"> <div class="topic-left-rail md-article-drawer position-relative d-flex border-right-sm border-left-sm open"> <div class="drawer d-flex flex-column open"> <div class="left-rail-section-content"> <div class="topic-left-rail-header text-truncate bg-gray-50 position-relative text-right d-flex align-items-center"> <div class="tlr-title px-20 py-15 text-left"> <em class="material-icons text-gray-400 d-lg-none" data-icon="toc"></em> <a class="font-serif font-weight-bold text-black link-blue" href="https://www.britannica.com/biography/Lee-de-Forest">Lee de Forest</a> </div> <button aria-label="Close" class="js-sections-close-button btn-link btn-sm btn d-lg-none position-absolute top-0 p-10 right-0" > <em class="material-icons font-26" data-icon="close"></em> </button> </div> <div class="section-content pl-10 pr-20 pl-sm-50 pr-sm-60 pl-lg-5 pr-lg-10 pt-10 pt-lg-0 bg-gray-50 clear-catfish-ad"> <div class="toc mb-20"> <div class="font-serif font-14 font-weight-bold mx-15 mb-15 mt-20"> Table of Contents </div> <ul class="list-unstyled my-0" data-level="h1"><li data-target="#ref1"><div class="pl-25"><a class="link-gray-900 w-100" href="/biography/Lee-de-Forest">Introduction</a></div><div class="ml-40 toc-drawer sub-toc-drawer"></div></li><li data-target="#ref1745"><div class="d-flex align-items-center"><div class="ml-25"></div><a class="w-100 link-gray-900" href="/biography/Lee-de-Forest#ref1745">Life</a></div><div class="ml-40 toc-drawer sub-toc-drawer"></div></li><li data-target="#ref1746"><div class="d-flex align-items-center"><div class="ml-25"></div><a class="w-100 link-gray-900" href="/biography/Lee-de-Forest#ref1746">Invention of the Audion tube</a></div><div class="ml-40 toc-drawer sub-toc-drawer"></div></li><li data-target="#ref1747"><div class="d-flex align-items-center"><div class="ml-25"></div><a class="w-100 link-gray-900" href="/biography/Lee-de-Forest#ref1747">Other inventions</a></div><div class="ml-40 toc-drawer sub-toc-drawer"></div></li></ul> <a class="toc-extra-link link-gray-900" href="https://www.britannica.com/biography/Lee-de-Forest/additional-info">References & Edit History</a> <a class="toc-extra-link link-gray-900" href="/facts/Lee-de-Forest">Quick Facts & Related Topics</a> </div> <div class="tlr-media-slider pb-10 mb-30"> <a class="section-header link-gray-900 font-serif font-14 font-weight-bold mb-10 mx-10" href="https://www.britannica.com/biography/Lee-de-Forest/images-videos">Images</a> <div class="slider js-slider position-relative d-inline-flex align-items-center mw-100 "> <div class="slider-container js-slider-container overflow-hidden d-flex overflow-hidden text-nowrap ml-15"> <a href="https://cdn.britannica.com/96/7996-004-3713DD17/Lee-De-Forest-1907.jpg" data-href="/media/1/153484/9889" class="media-overlay-link d-inline-block mr-5"> <img loading="lazy" src="https://cdn.britannica.com/96/7996-004-3713DD17/Lee-De-Forest-1907.jpg" alt="Lee De Forest, 1907." height="50" /> </a> <a href="https://cdn.britannica.com/75/79375-050-964CB201/Lee-De-Forest.jpg" data-href="/media/1/153484/97050" class="media-overlay-link d-inline-block mr-5"> <img loading="lazy" src="https://cdn.britannica.com/75/79375-004-6C8FDEBF/Lee-De-Forest.jpg" alt="De Forest, Lee" height="50" /> </a> <a href="https://cdn.britannica.com/04/159604-050-C26F3D7E/Lee-de-Forest.jpg" data-href="/media/1/153484/168294" class="media-overlay-link d-inline-block mr-5"> <img loading="lazy" src="https://cdn.britannica.com/04/159604-004-A1C399B8/Lee-de-Forest.jpg" alt="Lee de Forest." height="50" /> </a> <a href="https://cdn.britannica.com/08/143808-050-550CDF0D/De-Forest-Phonofilm-crew-grounds-White-House-1924.jpg" data-href="/media/1/153484/147462" class="media-overlay-link d-inline-block mr-5"> <img loading="lazy" src="https://cdn.britannica.com/08/143808-004-37B287EE/De-Forest-Phonofilm-crew-grounds-White-House-1924.jpg" alt="Phonofilm" height="50" /> </a> </div> <button disabled class="prev-button js-prev-button position-absolute btn btn-circle shadow btn-blue " aria-label="Previous"> <span class="material-icons md-24" data-icon="keyboard_arrow_left"></span> </button> <button disabled class="next-button js-next-button position-absolute btn btn-circle shadow btn-blue " aria-label="Next"> <span class="material-icons md-24" data-icon="keyboard_arrow_right"></span> </button> </div> </div> <div class="mb-30 tlr-student-links"> <div class="text-gray-900 p-5 font-serif font-14 font-weight-bold mx-10 mb-10"> For Students </div> <div class="imagelink-with-image-on-the-side card card-horizontal tlr-img-with-side-link ml-15 link-gray-900 mb-10" > <div class="position-relative card-media" style="flex: 0;"> <a class="ilf-image position-relative" href="/summary/Lee-de-Forest"> <img loading="lazy" src="https://cdn.britannica.com/mendel-resources/3-130/images/shared/default3.png?v=3.130.14" class="default " height="200" width="200"/> </a> </div> <div class="card-body ilf-content"> <a class="font-weight-semi-bold d-block mb-5 font-16 ilf-title" href="/summary/Lee-de-Forest" >Lee De Forest summary</a> </div> </div> </div> <div class="mb-30 tlr-related-quizzes"> <div class="text-gray-900 p-5 font-serif font-14 font-weight-bold mx-10 mb-10"> Quizzes </div> <div class="imagelink-with-image-on-the-side card card-horizontal tlr-img-with-side-link ml-15 link-gray-900 mb-10" > <div class="position-relative card-media" style="flex: 0;"> <a class="ilf-image position-relative" href="/quiz/a-history-of-everyday-technology-in-68-quiz-questions"> <img loading="lazy" 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Fielding</div> <div class="editor-description font-12 font-serif mt-5 clamp-description text-black">Dean, School of Motion Picture, Television and Recording Arts, Florida State University, Tallahassee. Editor of <i>A Technological History of Motion Pictures and Television.</i></div> </a> <div data-popper-arrow></div> </div> <span class="btn btn-link editor-link p-0 qa-byline-link gtm-byline font-12 byline-contributor text-decoration-underline"> Raymond E. Fielding</span></div> <div class="font-serif font-12 text-gray-700"> <span class="qa-fact-checked-by">Fact-checked by</span> <div class="editor-popover popover p-0"> <a class="d-block p-20 font-12" href="/editor/The-Editors-of-Encyclopaedia-Britannica/4419" > <div class="editor-title font-16 font-weight-bold">The Editors of Encyclopaedia Britannica</div> <div class="editor-description font-12 font-serif mt-5 text-black">Encyclopaedia Britannica's editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree. They write new content and verify and edit content received from contributors.</div> </a> <div data-popper-arrow></div> </div> <span class="btn btn-link editor-link p-0 qa-byline-link font-12 "> The Editors of Encyclopaedia Britannica</span></div> <div class="last-updated font-12 font-serif"> <a class="byline-edit-history" href="https://www.britannica.com/biography/Lee-de-Forest/additional-info#history" rel="nofollow">Article History</a> </div></div> </div> <button class="d-flex d-lg-none btn btn-outline-blue border rounded-sm shadow-sm mobile-toc-button gtm-mobile-toc-inline-button d-none d-sm-block js-sections-inline-button module-spacing btn d-lg-none"> <em class="material-icons mr-5 ml-n10 my-n5 md-icon" data-icon="toc"></em> Table of Contents </button> <div class="d-flex d-sm-none flex-row"> <button class="d-flex d-lg-none btn btn-outline-blue border rounded-sm shadow-sm mobile-toc-button gtm-mobile-toc-inline-button js-sections-inline-button module-spacing"> <em class="material-icons mr-5 ml-n10 my-n5 md-icon" data-icon="toc"></em> Table of Contents </button> <button class="ai-ask-button btn border-2 ai-ask-button btn border-2 module-spacing btn-sm js-inline-ai-ask-button btn-outline-red-400 border-red-400 p-10 ml-5"> Ask the Chatbot a Question </button> </div> <div class="js-qf-module qf-module px-40 px-sm-20 py-15 mx-auto module-spacing font-14 bg-gray-50 rounded"> <div class="qf-title font-weight-bold font-14 mb-10 text-center"> Quick Facts</div> <div class="facts-list mt-10"> <div class=""> <div class="js-fact mb-10 line-clamp clamp-3"> <dl> <dt>Born: </dt> <dd>August 26, 1873, <a href="/place/Council-Bluffs">Council Bluffs</a>, <a href="/place/Iowa-state">Iowa</a>, <a href="/place/United-States">U.S.</a></dd> </dl> <button class="js-more-btn d-none btn btn-unstyled font-12 bg-gray-50" aria-label="Toggle more/less fact data"> <em class="js-content link-blue">(Show more)</em> </button> </div> </div> <div class=""> <div class="js-fact mb-10 line-clamp clamp-3"> <dl> <dt>Died: </dt> <dd>June 30, 1961, Hollywood, <a href="/place/California-state">California</a> (aged 87)</dd> </dl> <button class="js-more-btn d-none btn btn-unstyled font-12 bg-gray-50" aria-label="Toggle more/less fact data"> <em class="js-content link-blue">(Show more)</em> </button> </div> </div> <div class=""> <div class="js-fact mb-10 line-clamp clamp-3"> <dl> <dt>Notable Family Members: </dt> <dd>spouse <a href="/biography/Nora-Stanton-Blatch-Barney">Nora Stanton Blatch Barney</a></dd> </dl> <button class="js-more-btn d-none btn btn-unstyled font-12 bg-gray-50" aria-label="Toggle more/less fact data"> <em class="js-content link-blue">(Show more)</em> </button> </div> <div class="text-center"> <a class="btn btn-sm btn-link p-0" href="/facts/Lee-de-Forest"> See all related content </a> </div> </div> </div> </div><span class="marker before-article"></span><section data-level="1" id="ref1"><span class="marker PREMOD1 mod-inline"></span><p class="topic-paragraph"><strong><span id="ref132992"></span>Lee de Forest</strong> (born August 26, 1873, <a href="https://www.britannica.com/place/Council-Bluffs" class="md-crosslink autoxref " data-show-preview="true">Council Bluffs</a>, <a href="https://www.britannica.com/place/Iowa-state" class="md-crosslink autoxref " data-show-preview="true">Iowa</a>, U.S.—died June 30, 1961, Hollywood, California) was an American inventor of the <a href="https://www.britannica.com/technology/Audion" class="md-crosslink " data-show-preview="true">Audion</a> vacuum tube, which made possible live <a href="https://www.britannica.com/topic/radio" class="md-crosslink autoxref " data-show-preview="true">radio</a> broadcasting and became the key component of all <a href="https://www.britannica.com/technology/radio-technology" class="md-crosslink " data-show-preview="true">radio</a>, <a href="https://www.britannica.com/technology/telephone" class="md-crosslink " data-show-preview="true">telephone</a>, <a href="https://www.britannica.com/technology/radar" class="md-crosslink " data-show-preview="true">radar</a>, <a href="https://www.britannica.com/technology/television-technology" class="md-crosslink " data-show-preview="true">television</a>, and <a href="https://www.britannica.com/technology/computer" class="md-crosslink " data-show-preview="true">computer</a> systems before the invention of the <a href="https://www.britannica.com/technology/transistor" class="md-crosslink " data-show-preview="true">transistor</a> in 1947. Although de Forest was bitter over the financial exploitation of his inventions by others, he was widely honoured as the “father of radio” and the “grandfather of television.” He was supported strongly but unsuccessfully for the <a href="https://www.britannica.com/topic/Nobel-Prize" class="md-crosslink " data-show-preview="true">Nobel Prize</a> for Physics.</p><span class="marker MOD1 mod-inline"></span></section> <span class="marker h2"></span><section data-level="1" id="ref1745"><h2 class="h1">Life</h2> <span class="marker PREMOD2 mod-inline"></span><p class="topic-paragraph">De Forest was the son of a <a href="https://www.britannica.com/topic/Congregationalism" class="md-crosslink " data-show-preview="true">Congregational</a> minister. His father moved the family to Alabama and there assumed the presidency of the nearly bankrupt <a href="https://www.britannica.com/place/Talladega" class="md-crosslink autoxref " data-show-preview="true">Talladega</a> College for Negroes. Ostracized by citizens of the white <a class="md-dictionary-link md-dictionary-tt-off mw" data-term="community" href="https://www.merriam-webster.com/dictionary/community" data-type="MW">community</a> who resented his father’s efforts to educate blacks, Lee made his friends from among the black children of the town and, together with his brother and sister, spent a happy although sternly <a class="md-dictionary-link md-dictionary-tt-off mw" data-term="disciplined" href="https://www.merriam-webster.com/dictionary/disciplined" data-type="MW">disciplined</a> childhood in this rural community.</p><span class="marker MOD2 mod-inline"></span> <span class="marker PREMOD3 mod-inline"></span><p class="topic-paragraph">As a child, he was fascinated with machinery and was often excited when hearing of the many technological advances during the late 19th century. By age 13 he was an enthusiastic inventor of mechanical gadgets, such as a miniature <a href="https://www.britannica.com/technology/blast-furnace" class="md-crosslink " data-show-preview="true">blast furnace</a> and <a href="https://www.britannica.com/technology/locomotive-vehicle" class="md-crosslink " data-show-preview="true">locomotive</a> and a working silver-plating apparatus.</p><a class="link-module shadow-sm d-block qa-quiz-module" href="/quiz/a-history-of-everyday-technology-in-68-quiz-questions" data-link-module-iframe-link=""> <img loading="lazy" src="https://cdn.britannica.com/18/171918-131-68E6E33A/Postcard-Alberto-Santos-Dumont-dirigible-Brazilian-Eiffel-Tower-October-19-1901.jpg" alt="Alberto Santos-Dumont. Postcard of Brazilian aviator Alberto Santos-Dumont's (1873-1932) airship or dirigible and Eiffel Tower. The Santos Dumont Air-Ship rounding the Eiffel Tower; on Octoboer 19th 1901. airplane" class="rounded-sm mr-15" width="70" /> <div class="line-clamp clamp-5"> <div class="module-title bg-green">Britannica Quiz</div> <div class="font-weight-semi-bold mt-5">A History of Everyday Technology in 68 Quiz Questions</div> </div> </a><span class="marker MOD3 mod-inline"></span> <span class="marker PREMOD4 mod-inline"></span><p class="topic-paragraph">His father had planned for him a career in the clergy, but Lee insisted on science and, in 1893, enrolled at the Sheffield Scientific School of <a href="https://www.britannica.com/topic/Yale-University" class="md-crosslink " data-show-preview="true">Yale University</a>, one of the few institutions in the <a href="https://www.britannica.com/place/United-States" class="md-crosslink autoxref " data-show-preview="true">United States</a> then offering a first-class scientific education. <a class="md-dictionary-link md-dictionary-tt-off mw" data-term="Frugal" href="https://www.merriam-webster.com/dictionary/Frugal" data-type="MW">Frugal</a> and hardworking, he supplemented his scholarship and the slim allowance provided by his parents by working at menial jobs during his college years, and, despite a not-too-distinguished undergraduate career, he went on to earn the Ph.D. in physics in 1899.</p><span class="marker MOD4 mod-inline"></span> <span class="marker PREMOD5 mod-inline"></span><p class="topic-paragraph">By this time he had become interested in electricity, particularly the study of electromagnetic-wave <a class="md-dictionary-link md-dictionary-tt-off mw" data-term="propagation" href="https://www.merriam-webster.com/dictionary/propagation" data-type="MW">propagation</a>, then being pioneered chiefly by the German <a href="https://www.britannica.com/biography/Heinrich-Hertz" class="md-crosslink " data-show-preview="true">Heinrich Rudolf Hertz</a> and the Italian <a href="https://www.britannica.com/biography/Guglielmo-Marconi" class="md-crosslink " data-show-preview="true">Guglielmo Marconi</a>. De Forest’s doctoral dissertation on the “Reflection of Hertzian Waves from the Ends of Parallel Wires” was possibly the first doctoral thesis in the United States on the subject that was later to become known as <span id="ref132993"></span><a href="https://www.britannica.com/technology/radio-technology" class="md-crosslink " data-show-preview="true">radio</a>.</p><span class="marker MOD5 mod-inline"></span> <span class="marker PREMOD6 mod-inline"></span><p class="topic-paragraph">His first job was with the <a href="https://www.britannica.com/money/Western-Electric-Company-Inc" class="md-crosslink " data-show-preview="true">Western Electric Company</a> in Chicago, where, beginning in the <a href="https://www.britannica.com/technology/electric-generator" class="md-crosslink " data-show-preview="true">dynamo</a> department, he worked his way up to the telephone section and then to the experimental laboratory. While working after hours on his own, he developed an electrolytic detector of <span id="ref132994"></span><a href="https://www.britannica.com/science/Hertzian-wave" class="md-crosslink ">Hertzian waves</a>. The device was modestly successful, as was an alternating-current transmitter that he designed. In 1902 he and his financial backers founded the De Forest Wireless Telegraph Company. In order to dramatize the potential of this new medium of communication, he began, as early as 1902, to give public demonstrations of wireless <a href="https://www.britannica.com/technology/telegraph" class="md-crosslink autoxref " data-show-preview="true">telegraphy</a> for businessmen, the press, and the military.</p><span class="marker MOD6 mod-inline"></span></section> <span class="marker h3"></span><section data-level="1" id="ref1746"><h2 class="h1">Invention of the <span id="ref132995"></span><a href="https://www.britannica.com/technology/Audion" class="md-crosslink " data-show-preview="true">Audion</a> tube</h2> <span class="marker PREMOD7 mod-inline"></span><div class="assemblies"><div class="w-100"><figure class="md-assembly m-0 mb-md-0 card card-borderless print-false" data-assembly-id="97050" data-asm-type="image"><div class="md-assembly-wrapper card-media " data-type="image"><a href="https://cdn.britannica.com/75/79375-050-964CB201/Lee-De-Forest.jpg" class="gtm-assembly-link position-relative d-flex align-items-center justify-content-center media-overlay-link card-media" data-href="/media/1/153484/97050"><picture><source media="(min-width: 680px)" srcset="https://cdn.britannica.com/75/79375-050-964CB201/Lee-De-Forest.jpg?w=300"><img src="https://cdn.britannica.com/75/79375-050-964CB201/Lee-De-Forest.jpg?w=300" alt="De Forest, Lee" data-width="1293" data-height="1600" loading="eager"></picture><button class="magnifying-glass btn btn-circle position-absolute shadow btn-white top-10 right-10" aria-label="Zoom in"><em class="material-icons link-blue" data-icon="zoom_in"></em></button></a></div><figcaption class="card-body"><div class="md-assembly-caption text-muted font-14 font-serif line-clamp"><span><a class="gtm-assembly-link md-assembly-title font-weight-bold d-inline font-sans-serif mr-5 media-overlay-link" href="https://cdn.britannica.com/75/79375-050-964CB201/Lee-De-Forest.jpg" data-href="/media/1/153484/97050">De Forest, Lee</a><span>Lee De Forest.</span><button class="js-more-btn d-none btn btn-unstyled font-12 bg-white js-content" aria-label="Toggle more/less fact data"><span class="link-blue">(more)</span></button></span></div></figcaption></figure></div></div><p class="topic-paragraph">A poor businessman and a poorer judge of men, de Forest was defrauded twice by his own business partners. By 1906 his first company was insolvent, and he had been squeezed out of its operation. But in 1907 he <a class="md-dictionary-link md-dictionary-tt-off eb" data-term="patented" href="https://www.britannica.com/dictionary/patented" data-type="EB">patented</a> a much more promising detector (developed in 1906), which he called the Audion; it was capable of more sensitive reception of wireless signals than were the electrolytic and Carborundum types then in use. It was a <span id="ref132996"></span><a href="https://www.britannica.com/technology/thermionic-power-converter" class="md-crosslink " data-show-preview="true">thermionic</a> grid-triode <span id="ref132997"></span><a href="https://www.britannica.com/technology/electron-tube" class="md-crosslink " data-show-preview="true">vacuum tube</a>—a three-element electronic “valve” similar to a two-element device patented by the Englishman <a href="https://www.britannica.com/biography/John-Ambrose-Fleming" class="md-crosslink " data-show-preview="true">Sir John Ambrose Fleming</a> in 1905. In 1907 de Forest was able to broadcast experimentally both speech and music to the general public in the <a href="https://www.britannica.com/place/New-York-City" class="md-crosslink autoxref " data-show-preview="true">New York City</a> area.</p><div class="module-spacing"> <DIV class="marketing-INLINE_SUBSCRIPTION marketing-content" data-marketing-id="INLINE_SUBSCRIPTION"><style> .student-promo-banner-wrapper { container-type: inline-size; margin-bottom: 15px; } @container (min-width: 475px) { .student-promo-banner { flex-direction: row; } .student-promo-banner-img-wrapper { margin-bottom: 0; margin-right: 10px; justify-content: flex-start; } .student-promo-banner-text-wrapper { text-align: left; margin-bottom: 0px; margin-left: 10px; } .student-promo-banner-button-wrapper { margin-right: 0; } }</style> <div class="student-promo-banner-wrapper"> <div class="student-promo-banner d-flex flex-column align-items-center bg-blue rounded p-20"> <div class="student-promo-banner-img-wrapper mb-20 mr-0 d-flex justify-content-center"> <img class="rounded" style="max-width: 100px; min-width: 80px" src="https://cdn.britannica.com/marketing/BlueThistle.webp" /> </div> <div class="student-promo-banner-text-wrapper ml-0 mb-10 text-center text-white"> <div class="h2 mb-10">Get Unlimited Access</div> <div class="h4 font-weight-semi-bold">Try Britannica Premium for free and discover more.</div> </div> <div class="student-promo-banner-button-wrapper d-flex justify-content-center align-items-center ml-auto mr-auto"> <a class="btn btn-m btn-orange" href="https://premium.britannica.com/premium-membership/?utm_source=premium&utm_medium=inline-cta&utm_campaign=black-friday-2024">Subscribe</a> </div> </div> </div> </DIV></div><span class="marker MOD7 mod-inline"></span> <span class="marker PREMOD8 mod-inline"></span><p class="topic-paragraph">A second company, the De Forest Radio Telephone Company, began to collapse in 1909, again because of some of his partners. In the succeeding legal confusion, de Forest was <a class="md-dictionary-link md-dictionary-tt-off eb" data-term="indicted" href="https://www.britannica.com/dictionary/indicted" data-type="EB">indicted</a> in 1912 but later acquitted of federal charges of using the mails to defraud by seeking to promote a “worthless device”—the Audion tube.</p><span class="marker MOD8 mod-inline"></span> <span class="marker PREMOD9 mod-inline"></span><p class="topic-paragraph">In 1910 he <span id="ref132998"></span><a href="https://www.britannica.com/technology/broadcasting" class="md-crosslink " data-show-preview="true">broadcast</a> a live performance by <a href="https://www.britannica.com/biography/Enrico-Caruso" class="md-crosslink " data-show-preview="true">Enrico Caruso</a> at the <a href="https://www.britannica.com/topic/Metropolitan-Opera-Association" class="md-crosslink autoxref " data-show-preview="true">Metropolitan Opera</a> in order to popularize the new medium further. In 1912 de Forest conceived the idea of “cascading” a series of Audion tubes so as to <span id="ref132999"></span><a href="https://www.britannica.com/technology/amplifier" class="md-crosslink " data-show-preview="true">amplify</a> high-frequency radio signals far beyond what could be accomplished by merely increasing the voltage on a single tube. He fed the output from the <a href="https://www.britannica.com/technology/anode" class="md-crosslink autoxref " data-show-preview="true">plate</a> of one tube through a transformer to the <a href="https://www.britannica.com/technology/grid" class="md-crosslink autoxref " data-show-preview="true">grid</a> of a second, the output of the second tube’s plate to the grid of a third, and so forth, which thereby allowed for an enormous amplification of a signal that was originally very weak. This was an essential development for both radio and telephonic long-distance communication. He also discovered in 1912 that by feeding part of the output of his <a href="https://www.britannica.com/technology/triode" class="md-crosslink autoxref " data-show-preview="true">triode</a> vacuum tube back into its grid, he could cause a self-regenerating oscillation in the <a href="https://www.britannica.com/technology/electric-circuit" class="md-crosslink autoxref " data-show-preview="true">circuit</a>. The signal from this <a class="md-dictionary-link md-dictionary-tt-off eb" data-term="circuit" href="https://www.britannica.com/dictionary/circuit" data-type="EB">circuit</a>, when fed to an antenna system, was far more powerful and effective than that of the crude transmitters then generally employed and, when properly modulated, was capable of <span id="ref133000"></span><a href="https://www.britannica.com/technology/transmitter" class="md-crosslink ">transmitting</a> speech and music. When appropriately modified, this single invention was capable of either transmitting, receiving, or amplifying radio signals.</p><span class="marker MOD9 mod-inline"></span> <span class="marker PREMOD10 mod-inline"></span><div class="assemblies"><div class="w-100"><figure class="md-assembly m-0 mb-md-0 card card-borderless print-false" data-assembly-id="168294" data-asm-type="image"><div class="md-assembly-wrapper card-media " data-type="image"><a href="https://cdn.britannica.com/04/159604-050-C26F3D7E/Lee-de-Forest.jpg" class="gtm-assembly-link position-relative d-flex align-items-center justify-content-center media-overlay-link card-media" data-href="/media/1/153484/168294"><picture><source media="(min-width: 680px)" srcset="https://cdn.britannica.com/04/159604-050-C26F3D7E/Lee-de-Forest.jpg?w=300"><img src="https://cdn.britannica.com/04/159604-050-C26F3D7E/Lee-de-Forest.jpg?w=300" alt="Lee de Forest." data-width="1600" data-height="1212" loading="eager"></picture><button class="magnifying-glass btn btn-circle position-absolute shadow btn-white top-10 right-10" aria-label="Zoom in"><em class="material-icons link-blue" data-icon="zoom_in"></em></button></a></div><figcaption class="card-body"><div class="md-assembly-caption text-muted font-14 font-serif line-clamp"><span><a class="gtm-assembly-link md-assembly-title font-weight-bold d-inline font-sans-serif mr-5 media-overlay-link" href="https://cdn.britannica.com/04/159604-050-C26F3D7E/Lee-de-Forest.jpg" data-href="/media/1/153484/168294">Lee de Forest. </a><button class="js-more-btn d-none btn btn-unstyled font-12 bg-white js-content" aria-label="Toggle more/less fact data"><span class="link-blue">(more)</span></button></span></div></figcaption></figure></div></div><p class="topic-paragraph">Throughout de Forest’s lifetime, the originality of his more important inventions was hotly contested by both scientists and patent attorneys. In time, realizing that he could not succeed in business or manufacturing, he reluctantly sold his patents to major communications firms for commercial development. Some of the most important of these sales were made at very low prices to the <a href="https://www.britannica.com/money/ATandT-Corporation" class="md-crosslink " data-show-preview="true">American Telephone & Telegraph Company</a>, which used the Audion as an essential amplification component for long-distance repeater <a class="md-dictionary-link md-dictionary-tt-off eb" data-term="circuits" href="https://www.britannica.com/dictionary/circuits" data-type="EB">circuits</a>.</p><div class="one-good-fact-module"> </div><span class="marker MOD10 mod-inline"></span></section> <span class="marker h4"></span><section data-level="1" id="ref1747"><h2 class="h1">Other inventions</h2> <span class="marker PREMOD11 mod-inline"></span><p class="topic-paragraph">In 1920 de Forest began to work on a practical system for <span id="ref133001"></span><a href="https://www.britannica.com/technology/sound-recording" class="md-crosslink " data-show-preview="true">recording</a> and reproducing sound <a href="https://www.britannica.com/art/motion-picture" class="md-crosslink " data-show-preview="true">motion pictures</a>. He developed a sound-on-film <span id="ref133002"></span><a href="https://www.britannica.com/technology/optical-sound-recording" class="md-crosslink " data-show-preview="true">optical recording</a> system called <span id="ref133003"></span><a href="https://www.britannica.com/technology/Phonofilm" class="md-crosslink " data-show-preview="true">Phonofilm</a> and demonstrated it in theatres between 1923 and 1927. Although it was basically correct in principle, its operating quality was poor, and he found himself unable to interest <span id="ref133004"></span><a href="https://www.britannica.com/technology/motion-picture-technology" class="md-crosslink " data-show-preview="true">film</a> producers in its possibilities. Paradoxically, within a few years’ time, the motion-picture industry converted to talking pictures by using a sound-on-film process similar to de Forest’s. During the 1930s de Forest developed Audion-diathermy machines for medical applications, and during <a href="https://www.britannica.com/event/World-War-II" class="md-crosslink autoxref " data-show-preview="true">World War II</a> he conducted military research for <a href="https://www.britannica.com/money/Bell-Laboratories" class="md-crosslink " data-show-preview="true">Bell Laboratories</a>.</p><span class="marker MOD11 mod-inline"></span> <span class="md-signature"><a href="/contributor/Raymond-E-Fielding/922">Raymond E. 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Lee de Forest | American Inventor & Radio Pioneer | Britannica