The Sunlight Transmitter

125 years back, June 3, 1880, Alexander Graham Bell made the first wireless phone call.

After installing a sunlight transmitter on a school 700 feet
away from a receiver in Bell's laboratory in Washington, his colleague Charles Summer Tainter said: "Mr. Bell, if you hear what I say, come to the window and wave your hat." And so he did.

The technology behind this first call was not radio, but sunlight. Bell's "photophone" had a vibrating mirror that could modulate a light beam to carry sound. Variation in resistance by selenium cells at the receiving end used to regenerate the sound.

Bell's and Tainter's invention came 15 years before Guglielmo Marconi's first successful radio transmission. The photophone's reliance on sunlight was one of the factors that prevented it from becoming a wireless success story.

Instead, as Mark Eckenwiler writes in the Post, the invention
"(...) laid the groundwork for the fibre-optic technology that today carries the bulk of Internet and telephone network traffic."

Neal McEwen, K5RW, at the "Telegraph Office", nmcewen@sbcglobal.net

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