Joseph Henry (1797-1878), whose bicentennial year has just been celebrated, is widely considered the foremost American scientist of the 19th century. In his youth, Henry appeared to be headed for a career in the theater, but a chance encounter with Lectures on Experimental Philosophy, Astronomy, and Chemistry by George Gregory turned his interest to science. Although Henry appears to have independently discovered the principle of electromagnetic induction at the same time that Michael Faraday did, Faraday's earlier publication of his results earned him, rather than Henry, credit for the discovery. Henry became the second president of the American Association for the Advancement of Science in 1849. He was also one of the founders of the National Academy of Sciences and became its second president in 1868.