The discovery of electromagnetic induction in the early part of the 19th century is one of the
greatest scientific achievements of all time, and it has had tremendous technological consequences.
The credit for this discovery rightfully goes to the great English experimental physicist Michael
Faraday. However, the American physicist Joseph Henry made some observations comparable to Faraday’s
at nearly the same time, and for that reason, Faraday and Henry are often considered to be
co-discoverers of some aspects of electromagnetic induction. We examine Henry’s early research on
electromagnetism, starting from his efforts to improve the electromagnet, which led directly to his
investigations of induction. We describe his earliest experiments on both mutual and self-induction,
and pay particular attention to the relationship of Henry’s research to that of Faraday. The
approach is one in which the experiments are described and then analysed using modern theory and
terminology.