Electronic Television — Invented at 21 by a Farm Boy Who Drew It in a Potato Field

Philo Farnsworth's 1930 patent describes the image dissector — the all-electronic camera tube that captured the first fully electronic television image, invented by a 14-year-old Idaho farm boy who conceived it while plowing rows of potatoes.

What it covers

This patent describes an electronic camera tube called an image dissector. A lens focuses an image onto a photosensitive surface (cathode) at one end of a vacuum tube. The photosensitive material emits electrons in proportion to the light intensity at each point — a process called the photoelectric effect. These electrons form an 'electron image' (a spatial pattern of electrons matching the light pattern of the original scene). A magnetic field deflects the entire electron image across a small aperture (the 'dissector aperture') — by varying the magnetic deflection, different points of the image are swept across the aperture sequentially, and a detector behind the aperture produces an electrical current proportional to the brightness at each scanned point. This current, varying over time, is the video signal.

What it doesn't cover

• —The cathode ray tube (CRT) display — Farnsworth's patent covers the camera pickup tube, not the display
• —Vladimir Zworykin's iconoscope (RCA's competing camera tube) — a different all-electronic design that RCA claimed predated Farnsworth's work
• —Color television — the image dissector was a black-and-white device; color encoding systems came later
• —Modern image sensors (CCD, CMOS) — solid-state electronic successors to vacuum tube camera technology

The clever bit

Farnsworth conceived the image dissector at age 14, in 1921, while plowing rows of potatoes on his family's farm in Rigby, Idaho. He realized that an image could be captured and transmitted electronically by scanning it line by line — exactly like the rows of crops he was plowing. He drew diagrams for his high school chemistry teacher, Justin Tolman, who later provided crucial testimony in the patent dispute with RCA. Farnsworth built a working prototype in 1927, at age 21, with funding from San Francisco investors. On September 7, 1927, he transmitted the first fully electronic television image — a single straight line. When his investors asked 'When are we going to see some dollars in this thing?', he transmitted a dollar sign.

Why it matters

Farnsworth is one of history's most poignant inventor stories. He conceived television at 14, built it at 21, won his patents against RCA, and licensed his technology — then watched as World War II halted commercial television development for six years, causing his patents to expire before he could profit from mass-market TV. He earned less from television than any major inventor of a world-changing technology. He suffered a breakdown in the 1940s and spent his later years working on nuclear fusion. He died in 1971, and his wife Elma ('Pem') said that when he first saw the moon landing on television — the culmination of a medium he invented — he turned to her and said it had all been worth it.

Real-world examples

• 1.The first fully electronic television image was transmitted by Farnsworth on September 7, 1927, in his lab at 202 Green Street, San Francisco — over 90 years before 4K TVs would display the same scene in 8 million pixels
• 2.RCA's David Sarnoff offered to buy Farnsworth's patents for $100,000 and hire him as an employee — Farnsworth refused; RCA instead launched a patent interference challenge that Farnsworth ultimately won based on his teacher's testimony and 1922 drawings
• 3.Farnsworth's patent victory forced RCA — the dominant electronics company of the era — to license his technology, one of the few times an independent inventor defeated a major corporation in a patent battle of this scale

Glossary