Alexander Graham Bell, in his lecture "On the Production and Reproduction of Sound by Light," presented the results of his and Sumner Tainter's experiments on photophones. They discovered that various substances, including gold, silver, platinum, iron, steel, brass, copper, zinc, lead, antimony, german-silver, Jenkin’s metal, Babbitt’s metal, ivory, celluloid, gutta-percha, hard rubber, soft vulcanized rubber, paper, parchment, wood, mica, and silvered glass, emit sounds when illuminated by light, with the pitch of the sound depending on the frequency of the light's vibration. They found that controlling the form or character of the light could produce articulate speech, allowing for wireless communication without the need for a conducting wire. Bell described the properties of selenium, a substance discovered by Berzelius in 1817, which is highly sensitive to light and can be used to detect changes in light intensity. He explained the historical development of selenium's properties and its applications in electrical conductivity. Bell and Tainter developed methods to reduce the resistance of selenium, making it more suitable for their photophone experiments. The lecture detailed the construction and operation of photophone transmitters and receivers, including the use of perforated plates, diaphragms, and mirrors to control the light beam. They demonstrated that sounds could be transmitted over distances, with the best results achieved using sunlight. They also explored the nature of the light rays that affect selenium, noting that the effects were not due to heat rays but to invisible rays. Bell concluded by expressing gratitude to the scientific community for their support and recognition, hoping that the same level of interest would be extended to the photophone as to the telephone.Alexander Graham Bell, in his lecture "On the Production and Reproduction of Sound by Light," presented the results of his and Sumner Tainter's experiments on photophones. They discovered that various substances, including gold, silver, platinum, iron, steel, brass, copper, zinc, lead, antimony, german-silver, Jenkin’s metal, Babbitt’s metal, ivory, celluloid, gutta-percha, hard rubber, soft vulcanized rubber, paper, parchment, wood, mica, and silvered glass, emit sounds when illuminated by light, with the pitch of the sound depending on the frequency of the light's vibration. They found that controlling the form or character of the light could produce articulate speech, allowing for wireless communication without the need for a conducting wire. Bell described the properties of selenium, a substance discovered by Berzelius in 1817, which is highly sensitive to light and can be used to detect changes in light intensity. He explained the historical development of selenium's properties and its applications in electrical conductivity. Bell and Tainter developed methods to reduce the resistance of selenium, making it more suitable for their photophone experiments. The lecture detailed the construction and operation of photophone transmitters and receivers, including the use of perforated plates, diaphragms, and mirrors to control the light beam. They demonstrated that sounds could be transmitted over distances, with the best results achieved using sunlight. They also explored the nature of the light rays that affect selenium, noting that the effects were not due to heat rays but to invisible rays. Bell concluded by expressing gratitude to the scientific community for their support and recognition, hoping that the same level of interest would be extended to the photophone as to the telephone.