Article XXXIV.—On the Production and Reproduction of Sound by Light; by Alexander Graham Bell, Ph.D. In presenting some discoveries made by Mr. Sumner Tainter and myself, which have resulted in the construction of apparatus for the production and reproduction of sound by means of light, it is necessary to explain the state of knowledge which formed the starting point of our experiments. We first describe the remarkable substance "selenium," and the manipulations devised by previous experimenters; but the final result of our researches has widened the class of substances sensitive to light vibrations, until we can propound the fact of such sensitiveness being a general property of all matter. We have found this property in gold, silver, platinum, iron, steel, brass, copper, zinc, lead, antimony, german-silver, Jenkins's metal, Babbitt's metal, ivory, celluloid, gutta-percha, hard rubber, soft vulcanized rubber, paper, parchment, wood, mica, and silvered glass; and the only substances from which we have not obtained results, are carbon and thin microscope glass. We find that when a vibratory beam of light falls upon these substances they emit sounds, the pitch of which depends upon the frequency of the vibratory change in the light. We find farther, that when we control the form or character of the light, vibrations on selenium (and probably on the other substances), we control the quality of the sound, and obtain all varieties of articulate speech. We can thus, without a conducting wire as in electric telephony, speak from station to station wherever we can project a beam of light. We have not had the opportunity of testing the limit to which this photophonic effect may be extended, but we have spoken to and from points 213 meters apart; and there seems no reason to doubt that the results will be obtained at whatever distance a beam of light can be flashed from one observatory to another. We shall now speak of selenium. Selenium was first discovered by Berzelius and Gottlieb Gahn in 1817. They observed a sediment in sulphuric acid that gave off a peculiar odor, like that attributed to tellurium. Berzelius attempted to produce tellurium from this deposit but failed. He found signs of sulphur mixed with mercury, copper, tin, zinc, iron, arsenic and lead, but no trace of tellurium. Berzelius, however, did not give up and continued his research, eventually discovering a new elementary substance, which he named selenium, from the Greek word for moon. Knox discovered in 1837 that selenium became a conductor when fused; and Hittorff showed in 1851 that it conducted at ordinary temperatures when in one of its allotropic forms. When selenium is rapidly cooled from a fused condition it is a non-conductor. In this, itsArticle XXXIV.—On the Production and Reproduction of Sound by Light; by Alexander Graham Bell, Ph.D. In presenting some discoveries made by Mr. Sumner Tainter and myself, which have resulted in the construction of apparatus for the production and reproduction of sound by means of light, it is necessary to explain the state of knowledge which formed the starting point of our experiments. We first describe the remarkable substance "selenium," and the manipulations devised by previous experimenters; but the final result of our researches has widened the class of substances sensitive to light vibrations, until we can propound the fact of such sensitiveness being a general property of all matter. We have found this property in gold, silver, platinum, iron, steel, brass, copper, zinc, lead, antimony, german-silver, Jenkins's metal, Babbitt's metal, ivory, celluloid, gutta-percha, hard rubber, soft vulcanized rubber, paper, parchment, wood, mica, and silvered glass; and the only substances from which we have not obtained results, are carbon and thin microscope glass. We find that when a vibratory beam of light falls upon these substances they emit sounds, the pitch of which depends upon the frequency of the vibratory change in the light. We find farther, that when we control the form or character of the light, vibrations on selenium (and probably on the other substances), we control the quality of the sound, and obtain all varieties of articulate speech. We can thus, without a conducting wire as in electric telephony, speak from station to station wherever we can project a beam of light. We have not had the opportunity of testing the limit to which this photophonic effect may be extended, but we have spoken to and from points 213 meters apart; and there seems no reason to doubt that the results will be obtained at whatever distance a beam of light can be flashed from one observatory to another. We shall now speak of selenium. Selenium was first discovered by Berzelius and Gottlieb Gahn in 1817. They observed a sediment in sulphuric acid that gave off a peculiar odor, like that attributed to tellurium. Berzelius attempted to produce tellurium from this deposit but failed. He found signs of sulphur mixed with mercury, copper, tin, zinc, iron, arsenic and lead, but no trace of tellurium. Berzelius, however, did not give up and continued his research, eventually discovering a new elementary substance, which he named selenium, from the Greek word for moon. Knox discovered in 1837 that selenium became a conductor when fused; and Hittorff showed in 1851 that it conducted at ordinary temperatures when in one of its allotropic forms. When selenium is rapidly cooled from a fused condition it is a non-conductor. In this, its