Hall Effect in Semiconductors

“One day in the year of 1820, walking to his lecture at the University of Copenhagen, Oersted got an idea. If static electricity did not affect magnets in any way, maybe things would be different if one tried electricity moving through the wire connecting the two poles of the Volta pile. Arriving at the classroom filled with a crowd of young students, Oersted placed on the lecture table his Volta pile, connected the two opposite ends of it by a platinum wire, and placed a compass needle close to it. The needle, which was supposed to orient itself always in the north-south direction, turned around and came to rest in the direction perpendicular to the wire. The audience was not impressed but Oersted was.”