photoelectric effect discovered by Albert Einstein in 1905. He wrote to Einstein about it, but did not receive a reply. Losev designed practical carborundum electroluminescent lights, but found no one interested in commercially producing these weak light sources. Losev died in World War II. Due partly to the fact that his papers were published in Russian and German, and partly to his lack of reputation (his upper class birth barred him from a college education or career advancement in Soviet society, so he never held an official position higher than technician) his work is not well known in the West. Use during the broadcast era In the 1920s, the amplifying triode vacuum tube, invented in 1907 by Lee De Forest, replaced earlier technology in both radio transmitters and receivers. AM radio broadcasting spontaneously arose around 1920, and radio listening exploded to become a hugely popular pastime. The initial listening audience for the new broadcasting stations was probably largely owners of crystal radios. But lacking amplification, crystal radios had to be listened to with earphones, and could only receive nearby local stations. The amplifying vacuum tube radios which began to be mass-produced in 1921 had greater reception range, did not require the fussy adjustment of a cat whisker, and produced enough audio output power to drive loudspeakers, allowing the entire family to listen comfortably together, or dance to Jazz Age music. So during the 1920s vacuum tube receivers replaced crystal radios in all except poor households. Commercial and military wireless telegraphy stations had already switched to more sensitive vacuum tube receivers. Vacuum tubes temporarily put an end to crystal detector research. The temperamental, unreliable action of the crystal detector had always been a barrier to its acceptance as a standard component in commercial radio equipment and was one reason for its rapid replacement. Frederick Seitz, an early semiconductor researcher, wrote: The crystal radio became a cheap alternative receiver used in emergencies and by people who couldn't afford tube radios: teenagers, the poor, and those in developing countries. Building a crystal set remained a popular educational project to introduce people to radio, used by organizations like the Boy Scouts. The galena detector, the most widely used type among amateurs, became virtually the only detector used in crystal radios from this point on. The carborundum junction saw some use as a detector in early vacuum tube radios because it was more sensitive than