It has been but a short time since both the scientific and the financial worlds were astounded by the actual transmission of intelligible wireless signals across the Atlantic, and the name of Marconi will go down to posterity as the one who first accomplished this great feat.
The principal limit to the distance of transmission lies in the delicacy of the receiving instruments. The most sensitive are those in which a telephone receiver forms a part of the receiving apparatus. The almost incredibly small amount of electric energy required to produce intelligible speech in an ordinary Bell telephone receiver nearly passes belief. The work done in lifting such an instrument from its hook to the ear of the listener, would, if converted into electric energy, be sufficient to maintain an audible sound in a telephone for 240,000 years! Even extremely attenuated waves may therefore produce audible signals in such a receiver.
The electric motor was another gift of Faraday to commercial science, although in this case there are others who can, perhaps, justly claim to share the honor with him. Faraday's early electric motor consisted essentially in a device whereby a movable conductor, suspended so as to be capable of rotation around a magnet pole, was caused to rotate by the mutual interaction of the magnetic fields of the active conductor and the magnet. The magnet, which consisted of a bar of hardened steel, was fixed in a cork stopper, which completely closed the end of an upright glass tube. A small quantity of mercury was placed in the lower end of the tube, so as to form a liquid contact for the lower end of a movable wire, suspended so as to be capable of rotating at its lower extremity about the axis of the tube. On the passage of an electric current through the wire, a continuous rotary motion was produced in it, the direction of which depends both on the direction of the current, and on the polarity of the end of the magnet around which the rotation occurs.
The great value of the electric motor to the world is too evident to need any proof. The number of purposes for which electric motors are now employed is so great that the actual number of motors in daily use is almost incredible, and every year sees this number rapidly increasing.
The above are the more important machines or devices that have been directly derived from Faraday's great investigation as to the production of electricity from magnetism. Let us now inquire briefly as to what useful processes or industries have been rendered possible by the existence of these machines.
Apparently one of the most marked requirements of our twentieth-century civilization is that man shall be readily able to extend the day far into the night. He can no longer go to sleep when the sun sets, and keep abreast with his competitors. Of all artificial illuminants yet employed, the arc and the incandescent electric lights are unquestionably the best, whether from a sanitary, aesthetic, or truest economical standpoint. Now, while it is a well-known matter of record that both arc and incandescent lights were invented long before Faraday's time, yet it was not until a source of electricity was invented, superior both in economy and convenience to the voltaic battery, that either of these lights became commercial possibilities. Such an electric source was given to the world by Faraday through his invention of the dynamo-electric machine, and it was not until this machine was sufficiently developed and improved that commercial electric lighting became possible. The energy of burning coal, through the steam-engine, working the dynamo, is far cheaper and more efficient for producing electricity than the consumption of metals through the voltaic pile.
It is characteristic of the modesty of Faraday that when, in after-life, he heard inventors speaking of their electric lights, he refrained from claiming the electric light as his own, although, without the machine he taught the world how to construct, commercial lighting would have been an impossibility.
The marvellous activity in the electric arts and sciences, which followed as a natural result of Faraday giving to the world in the dynamo-electric machine a cheap electric source, naturally leads to the inquiry as to whether at a somewhat later day a yet greater revolution may not follow the production of a still cheaper electric source. In point of fact such a discovery is by no means an impossibility. When a dynamo-electric machine is caused to produce an electric current by the intervention of a steam-engine, the transformation of energy which takes place from the energy of the coal to electric energy is an extremely wasteful one. Could some practical method be discovered by means of which the burning of coal liberates electric energy, instead of heat energy, an electric source would be discovered that would far exceed in economy the best dynamo in existence. With such a discovery what the results would be no one can say; this much is certain, that it would, among other things, relegate the steam-engine to the scrap-heap, and solve the problem of aerial navigation.
What is justly regarded as one of the greatest achievements of modern times is the electrical transmission of power over comparatively great distances. At some cheap source of energy, say, at a waterfall, a waterwheel is employed to drive a dynamo or generator, thus converting mechanical energy into electrical energy. This electricity is passed over a conducting line to a distant station, where it is either directly utilized for the purpose of lighting, heating, chemical decomposition, etc., or indirectly utilized for the purpose of obtaining mechanical power for driving machinery, by passing it through an electric motor. The electric transmission of power has been successfully made in California over a distance of some 220 miles, at a pressure on transmission lines of 50,000 volts.
The high pressures required for the economical use of transmission lines necessitates the employment of transformers at each end of the line; namely, step-up transformers at the transmitting end, to raise the voltage delivered by the generators, and step-down transformers, at the receiving end, to lower it for use in the various translating devices. These transformers are employed in connection with alternating-current dynamos. Faraday not only gave to the world the first electric generator, but also the first transformer, and one of the first electric motors, and without these gifts the electric transmission of power over long distances, which has justly been regarded as one of the most marvellous achievements of our age, would have been an impossibility.