In 1835, Thomas Davenport, an American blacksmith, made the world's first practical motor that could drive a small trolley. In the early 1870s, the world's earliest commercial motor was invented by Belgian electrical engineer Zenobe Theophile Gamme. In 1888, the famous American inventor Nikola Tesla applied Faraday's electromagnetic induction principle to invent an AC motor, which is an induction motor. In 1845, British physicist Wheatstone applied for a patent for a linear motor, but the principle was only taken seriously in the 1960s, and practical linear motors were designed and have been widely used in industry. In 1902, Swedish engineer Danielson invented the synchronous motor using the rotating magnetic field concept of Tesla's induction motor. In 1923, Scotsman James Weir French invented the three-phase variable reluctance stepper motor. In 1962, with the help of Hall elements, a practical DC brushless motor finally came out. In the 1980s, practical ultrasonic motors began to appear.