Overview
Philo Taylor Farnsworth (1906–1971) built the image dissector, the first camera tube to convert an optical image into an electrical signal entirely electronically, transmitting his first image — a single straight line — on 7 September 1927. In 1935 the US Patent Office awarded him priority over RCA's Zworykin; RCA appealed and lost, and licensed his patents in 1939. His foundational patent expired in August 1947, before American television became a mass medium.
What You Need
- Lived: 1906–1971, United States
- Anchor year: 1927 — first electronic image transmission, 7 September
- Strand: canon — and routinely mis-told
Steps
The problem as it stood
By the mid-1920s the display end of television could be done electronically, but every working camera used a spinning disc. What was missing was a way to convert a whole optical image into a signal with no moving parts.
What he actually did
Farnsworth filed his foundational patent on 7 January 1927; it issued as US 1,773,980 on 26 August 1930. On 7 September 1927, at 202 Green Street in San Francisco, his image dissector transmitted its first image between rooms — a single straight line. He had sketched the principle as a schoolboy, a drawing his chemistry teacher Justin Tolman later produced in evidence.
How it worked
The image dissector focuses the optical image onto a photocathode, which emits an electron image. Magnetic fields sweep that entire electron image across a small aperture, so each part of the picture passes the aperture in turn and is measured. It is genuinely electronic with no moving parts — but it has no charge storage, so it reads each point only as it passes and needs very bright light.
What it made possible
The image dissector established that fully electronic television was real, and Farnsworth's patents were strong enough that RCA — a company that collected royalties rather than paying them — had to take a licence. The dissector itself found long service in industrial and military applications where light was plentiful.
What happened to him
RCA licensed his patents in 1939, reportedly the first time it had paid patent royalties. The patent then ran its 17-year term from grant and expired in August 1947 — before the postwar television boom. He later worked on nuclear fusion, and died in 1971.
Where the credit landed
In 1935 the US Patent Office awarded priority for the electronic "electrical image" claim to Farnsworth over RCA's Zworykin, and RCA lost its appeal; in 1939 RCA licensed Farnsworth's patents. Farnsworth's foundational patent nonetheless expired in 1947, before television became a mass medium, and the tube that made broadcast television practical was Zworykin's charge-storage iconoscope rather than Farnsworth's image dissector. Both men are essential to the story and neither invented television alone.
Pro Tips
- Farnsworth won the patent interference — dramatisations that show him losing are wrong.
- Winning the patent and winning the industry are different things, and he did only the first.
- The image dissector had no charge storage, which is precisely why the iconoscope displaced it.
Knowledge Base
What You'll Learn
The Farnsworth story is usually told as a wronged genius narrative. The documented version is stranger and more interesting.
The interference, precisely
RCA brought a patent interference against Farnsworth. The Patent Office decided Interference No. 64,027 in 1935, awarding priority to Farnsworth, turning principally on Claim 15 of US 1,773,980 — the concept of an "electrical image". Justin Tolman testified and produced the schoolboy sketch. RCA appealed and lost, and licensed in 1939.
What is genuinely contested
The $1,000,000 figure for the 1939 licence is repeated everywhere but no contemporaneous document for it has been found, and sources differ on whether it was signed in September or December 1939 — treat both as reported rather than established. Whether Zworykin's 1930 visit to Farnsworth's laboratory materially advanced RCA's iconoscope is also disputed: the iconoscope is a charge-storage tube of a different family from the image dissector, so a lab visit does not straightforwardly explain it.
Where This Fits
This guide covers one specific part of the history of media technology. The wider picture — how each link in the chain from capture through transmission to display was actually built, who built it, and why the credit so often landed somewhere else — is in A History of Broadcast Technology: The Chain From Capture to Screen, which frames the discipline as a whole and links out to the detailed guides underneath it, including this one. If you are starting from scratch rather than solving a specific problem, read that first and come back here.
FAQ
Q: Did Farnsworth win against RCA?
A: Yes. The US Patent Office awarded him priority in Interference No. 64,027 in 1935, RCA appealed and lost, and RCA licensed his patents in 1939. Dramatisations showing him losing the case are incorrect.
Q: If he won, why is he not famous the way Edison is?
A: His foundational patent expired in August 1947, before the postwar television boom, so he earned little from the medium's mass adoption. And the camera tube the industry actually used was Zworykin's iconoscope, which works on charge storage — a different principle from the image dissector.
Q: Did Zworykin steal the design during his 1930 lab visit?
A: Disputed. Farnsworth partisans treat the visit as effectively industrial espionage; other accounts note the iconoscope is a charge-storage tube of a different family from the image dissector, so the visit does not straightforwardly account for it.