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,