. The theoretical foundation was laid in the early 1830s, with the independent discovery of electromagnetic induction by Michael Faraday and Joseph Henry. They showed that a changing magnetic field can induce a current of a higher voltage (known as “stepping up”) or a lower one (“stepping down”). But it took another half-century before Lucien Gaulard, John Dixon Gibbs, Charles Brush, and Sebastian Ziani de Ferranti could design the first useful transformer prototypes. Next, a trio of Hungarian engineers—Ottó Bláthy, Miksa Déri, and Károly Zipernowsky—improved the design by building a toroidal (doughnut-shaped) transformer, which they exhibited in 1885.