During the summer of 1881, we published an article by the father of the telephone himself: Alexander Graham Bell. The eminent Scottish inventor, who unveiled his telephone just five years earlier, told us about the challenges of producing a clear sound across all devices. Selenium, which had initially yielded the clearest sound when hit with a beam of light, was not reliable. While experimenting, Bell found that two pieces of selenium rarely produced the same quality of sound, even when those two pieces came from the same stick.
His cousin, Chichester Bell, suggested that Bell's selenium samples was contaminated with other chemicals. Another possible solution came from Professor W.G. Adams, who demonstrated "that tellurium, like selenium, has its electrical resistance affected by the light." When the Bells attempted to build cells using tellurium (pictured on the left) instead of selenium, they found that the substance was a little too sensitive to light. Instead of becoming discouraged, however, they decided to experiment with alloys of tellurium and selenium.
Read the full story in Production of Sound by Radiant Energy