at right angles to one another.
While current travels from z to y—that is, from the ring C1 to y—it also travels from x to w, because w x rises while y z descends. So that a current circulates through the coil and the exterior part of the circuit, including the lamp. After z y has passed the lowest possible point of the circle it begins to ascend, w x to descend. The direction of the current is therefore reversed; and as the change is repeated every half-revolution this form of dynamo is called an alternator or creator of alternating currents. A well-known type of alternator is the magneto machine which sends shocks through any one who completes the external circuit by holding the brass handles connected by wires to the brushes. The faster the handle of the machine is turned the more frequent is the alternation, and the stronger the current.
CONTINUOUS-CURRENT DYNAMOS.
An alternating current is not so convenient for some purposes as a continuous current. It is therefore sometimes desirable (even necessary) to convert the alternating into a uni-directional or continuous current. How this is done is shown in Figs. 69 and 70. In place of the two collecting rings C C 1 , we now have a single ring split longitudinally into two portions, one of which is connected to each end of the coil w x y z . In Fig. 69 brush B has just passed the gap on to segment C, brush B 1 on to segment C 1 . For half a revolution these remain respectively in contact; then, just as y z begins to rise and w x to descend, the brushes cross the gaps again and exchange segments, so that the