Correspondence

Invention of solid-state amplifier — In an article in the February issue of Physics Today, Professor Virgil E. Bottom calls attention to several patents of Julius E. Lilienfeld (recently deceased) relating to devices for “amplifying and controlling electric currents.” The remarkable thing about these patents is the dates — filed in 1926 and 1928 and issued in 1930–1933. Prof. Bottom incorrectly considers the devices to be n-p-n transistors. There is no doubt that they are field-effect transistors using n-type Cu2S as the semiconductor.