Page:Electricity (1912) Kapp.djvu/226

222 the internal part of the path is likewise reduced considerably by making the internal cylinder not entirely of copper, but using an iron cylinder with a mere coating of copper. Thus there is only the narrow space left between the two cylinders where the lines of force have to be forced across a non-magnetic medium, and the result is a very large increase in the total magnetic flux. At the moment that the current in coil A has crest value the flux has the direction as indicated by the arrow 1. A moment later, when B also becomes active, the direction of the flux is shown by the arrow 2. A quarter period later when the current in A is zero and that in B has crest value, the flux is due to B only and has the direction 3. A little later still the current in B has diminished and that in A has grown to some negative value. Thus the flux is turned into the position 4 and so on, the flux gradually passing through the directions given by the arrows 5, 6,7,8, and then the cycle begins again.

The motor shown in Fig. 24 has still an imperfection. No definite path is provided for the current induced in the revolving cylinder, technically termed the "rotor." The currents flow more or less irregularly within the whole mass of the metal, and some