Crystal radio detector ["cat's whisker"]: the first wireless device

Summary form only given. The discovery of the crystal detector by Ferdinand Braun in 1874 is briefly discussed. Braun's interest in the electrical conductivity of metal salts in solution (electrolytes) ultimately led to his study of metal sulfide crystals and other crystalline solids, which conduct even when not dissolved. After much experimentation, Braun reported in 1874 (Annalen der Physik und Chemie, November 23, 1874) that for many metal sulfides the electrical resistance varies with the magnitude and polarity of the applied voltage. Galena Crystal, composed of lead sulfide, was used in his work.