In the generation of this mighty force improvements have been made, but those of greatest power still involve the principles discovered by Faraday and Henry seventy years ago. The ideas of Faraday of the “lines of force”--the magnetic power streaming from the poles of the magnet somewhat as the rays of heat issue on all sides from a hot body, forming the magnetic field--and that a magnet behaves like an electric current, producing an electric wave by its approach to or recession from a coil of wire, joined with Henry’s idea of increasing the magnetising effect by increasing the number of coils around the magnet, enter into all powerful dynamo electric machines of to-day. In them the lines of force must flow around the frame and across the path of the armature; and there must be a set of conductors to cut the lines of force twice in every revolution of the cylinder carrying the armature from which the current is taken. When machines had been produced for generating with some economy powerful currents of electricity, their use for the world’s business purposes rapidly increased. Among such applications, and following closely the electric lighting, came the _electric railway_. A substitute for the slow animal, horse, and for the dangerous, noisy steam horse and its lumbering locomotive and train, was hailed with delight. Inventors came forward with adaptations of all the old systems they could think of for the purpose, and with many new ones. One plan was to adapt the storage battery--that silent chemical monster which carries its own power and its own machine--and place one on each car to actuate a motor connected to the driving wheels. Another plan was to conduct the current from the dynamo machine at its station along the rails on one side of the track to the motor on the car and the return current on the opposite track; another was to carry the current to the car on a third rail between the track, using both the other rails for the return; another to use an overhead wire for the current from the dynamo, and connect it with the car by a rod, one end of which had a little wheel or trolley running on the overhead wire, to take up the current, the other end being connected by a wire to the car motor; another plan to have a trench made leading from the central station underneath the track the whole length of the line, and put into this trench conducting wires from the dynamo, to one of which the car motor should be connected by a trolley rod or “brush,” extending down through a central slot between the rails of the track to carry the electric supply into the motor. In all these cases a lever was supplied to cut off communication between the conducting wire and the motor, and a brake lever to stop the car. All of these plans have been tried, and some of them are still being tried with many improvements in detail, but not in principle.