[Gk.] A machine used for generating a current of electricity by the rotation of coils of wire with iron cores between the poles of a powerful electro-magnet. When any conductor of electricity is moved about in the space surrounding the poles of a magnet so as to cut the lines of force at right angles, currents of electricity are produced in the conductor. In magneto-electric machines permanent magnets are used; but when an electro-magnet is substituted for the permanent magnet, the machines are termed "dynamos," or dynamo-electric machines. Dynamos are used for electric lighting; also to operate electric motors on cars and in factories to drive machinery - the motor being simply a reversed dynamo.