DYNAMO - ELECTRIC MACHINERY. :\lachinery in which mechanical energy is con verted into electrical energy, or vice versa. by means of magnetic induction. According to this definition, every dynamo-electric machine is capa ble of serving either as a generator or as a motor, according to it is supplied with mechanical or electrical energy and W het her it is, therefore, giving out electrical or mechanical energy. respectively. In an electric gencralw incelianien1 energy is converted into electrical energy by means of continuous relative motion between electrical conductors and a magnetic field, or fields. such motion causing the conduc tors to cut or traverse the lines of force of the fields. In an electric motor electrical energy is transformed into mechanical energy by means of continuously supplying a system of electrical conductors with an electric current, which causes a magnetic force to act between the eonductors carrying it and the magnetic field, or fields, thereby producing continuous relative 'notion he ti\ een the conductors and the magnetic fields.
The preceding definitions are general and iwe essaril• technical. To comprehend them fully a knowledge of the fundamental principles in volved in the operation of dynamo-eleetrie machines is necessary. They may, however, be in a measure elucidated by a descriptive defini tion as follows: All generators consist essentially of one or more eleetro-magnets between the poles of which an armature, consisting of a soft iron core wound with coils of insulated copper wire, is made to revolve very rapidly by means of a steam-engine, a water-wheel, or other prime mover. In the transmission of energy by elec
tricity the current produced by the generator is made to pass through another machine, similar and often identical in construction, and there causes the armature to revolve, and this revolu tion may be employed to do any kind of me chanical work. This second machine, working in reverse order from the first, is an electric motor. This description makes it clear, as do the pre ceding definitions, that to understand thorough ly the dynamo-electric machine requires a knowledge of three great branches of science— magnetism, electricity, and mechanics. The necessity for this special lalowledge makes the subject of dynamo-electric machines a difficult one to discuss in universally familiar terms. At best, therefore, only an indication of the structural details and operating principles in volved is possible when the demonstrator is lim ited by such restrictions.