The discovery that an electric current would produce a magnet suggested to Michael Faraday, of the Royal Institution at London, the question, Will a magnet produce an electric current? He kept asking himself this question over and over again. Oersted had changed electricity into magnetism. Faraday set about doing the opposite, change magnetism into electricity. He first tried to do this in 1822, but failed. He also failed in three other attempts. In the year 1831 he took up the problem for the fifth time. He coiled 220 feet of wire around a pasteboard tube and connected the ends of the coil to an instrument which would show if there was an electric current flowing. Taking a round bar magnet eight and a half inches long and three fourths of an inch in diameter, he thrust it quickly full length into the coil. The needle of the instrument showed that there was a current, but the current stopped when the magnet came to rest. He jerked the magnet out, and again the needle moved, but in the opposite direction. The needle swung back and forth each time the magnet was thrust in and out, but there was no movement when the magnet was still.

Faraday at last, after five attempts, succeeded in producing an electric current from a magnet. He saw why he had failed before. In his earlier attempts, the coil of wire and the magnet were left at rest. A magnet might lie in or by a coil of wire for a hundred years, and no electric current would come from it. The electric current, as Faraday had learned, is produced by the magnet when in motion, or when the wire coil breaks through the currents of magnetism coming from the magnet.

Faraday now saw how to make a new machine to generate electricity. A copper disk twelve inches in diameter and a fifth of an inch thick was fastened on a brass axle. This was so mounted that the disk could be turned rapidly. A powerful permanent horseshoe magnet was placed so that the disk revolved between its two ends. A metal collector was held again the edge of the disk, and a second collector was fastened to the axle. Faraday turned the disk, and a steady current of electricity was produced. This was the first dynamo ever made.

By persevering until he found out how to produce an electric current from a magnet, Faraday blazed the way for some wonderful inventions. Without the dynamo to generate the electricity, we should not have electric lights, electric street cars, electric railroads, or electric-driven machines in factories.

There are two parts to every dynamo, the magnet and the whirling disk. The electricity is produced by the disk, called the armature, breaking through or across the currents of magnetism coming from the magnet.

The currents of magnetism in Faraday's dynamo were supplied by a permanent magnet. But the electromagnet supplies a more powerful magnetic field than the strongest permanent magnet; therefore in all the dynamos of to-day, electromagnets are employed. In the very largest dynamos there are a number of these, each more powerful than the strongest one made by Henry.

The armature in Faraday's dynamo was merely a copper disk. Present-day armatures are made up of a core or inner portion, and the windings of copper wire over the core. The core in the common armature is made up of a great number of very thin and soft sheet-iron disks. Around these are wound many thousand turns of copper wire.

Between the time when Faraday made the first dynamo and the present, many men worked to make the dynamo useful, that is, to make one which would produce electricity in large quantities and at a small cost. Among these experimenters are to be counted Siemens of Germany, and Edison of America. Under the careful and patient work of these and other men, the simple dynamo of Faraday grew into the monsters of to-day. From these monster dynamos, hidden away in some remote power house, comes the electric current to light our homes and streets, to drive the machines of mills and factories, to propel street cars, to haul passenger trains, and even to cook our food.

What was now needed was a machine, a motor, that would convert electricity into power which could be used to turn all kinds of machines. Toy motors were made as early as 1826. But a practical motor, even if a good one had been invented, was not possible until the dynamo had been perfected, and cheap electricity was to be had.

In 1873 there was an Industrial Exhibition at Vienna, Austria, where a number of dynamos were displayed. One day an absent-minded workman connected the wires of a dynamo which was running, to one that was standing still. To his surprise the armature began to spin around. It was thus discovered by accident that the dynamo, invented to produce electricity, could be used also to change electricity into power, or that the dynamo is also a motor. Dynamos and motors are now built almost alike, but motors do not have to be as large and heavy as dynamos. It thus came about that the men who perfected the dynamo, at the same time, without knowing it, perfected the motor.

The motor was immediately put to work. At the Industrial Exposition at Berlin, in 1879, Dr. Siemens exhibited a small electric locomotive drawing a train of three small cars. The track, about a thousand feet long, was circular, and for this reason the first electric railway was called "Siemens's electrical merry-go-round." In 1881, Dr. Siemens built a street-car line a mile and a half long. A motor was fastened between the axles of an old horse car, and a dynamo exactly like the motor on the car was set up to furnish the electricity. The new electric line easily drove the omnibus from the street. Electric street railways were soon being operated in all parts of the civilized world, and no sight to-day is more familiar than the trolley car.

Edison was quick to see the practical importance of the motor, and on hearing of Dr. Siemens's "electrical merry-go-round" set to work. His first electric locomotive was built early in 1880. It was made up of an ordinary flat dump car, on which was mounted a dynamo for a motor, known as "A Long-waisted Mary Ann." Improvements quickly followed, and it was not many months before his motors were ready to propel street cars. The first electric street railway in America was built at Baltimore, in 1885.

Edison was also among the first to see that electric locomotives could be built large enough to draw freight and passenger trains, and by 1882 he had a big electric locomotive on exhibition at Menlo Park. Considerable use is now made of electric locomotives for hauling trains in and out of large cities, and on a few railroads they have taken the place of steam locomotives, either altogether or in part.

Besides being employed to propel trolley cars and locomotives, a great many motors are used in mills and factories to drive machinery. But it must not be supposed that all motors are large and powerful. They are of almost every imaginable size, from the great monsters in electric locomotives, down to the little motor that is just strong enough to run a sewing machine, or whirl an electric fan, or propel a toy engine.