Joseph Henry (December 17, 1797 - May 13, 1878) was an American scientist. While building electromagnets, Henry discovered the electromagnetic phenomenon of self-inductance. He also discovered mutual inductance independently of Michael Faraday, though Faraday was the first to publish his results. The SI unit of inductance, the henry, is named in his honor. Henry's work on the electromagnetic relay was the basis of the electrical telegraph. Henry identified the room acoustics phenomena we now call direct sound, early reflections, and reverberation. He demonstrated the early sound integration period and laid the groundwork for further fundamental research on early reflections. He died in 1878 at the age of 80. This image has been color-enhanced.