The principle of conservation of energy, now so well known and universally accepted, was then but a vague guess in the minds of the more advanced in science.  Faraday was among the first to accept the new doctrine, and many of his brilliant discoveries were made in his effort to prove the truth of these important generalizations.  He was acquainted with Sturgeon’s method of making magnets by sending a current of electricity through a wire wound around a bar of iron; and he reasoned, if electricity will make a magnet, a magnet ought to make electricity.  As early as 1821 his note book contains this suggestion:  “Convert magnetism into electricity.”  Again and again he attacked the problem; but it was not until the autumn of 1831 that his efforts to solve it were successful.  Then in a series of experiments that have scarcely ever been equaled in brilliancy and originality, he gave to the world the principle on which is based the wonderful development of modern electrical science.

The principle is briefly stated.  The space, around a wire carrying an electric current, or in the neighborhood of a magnet, has a directive effect upon a magnetic needle, and is hence called a magnetic field.  Now if a conductor, or coil of wire, be placed in the field across the direction of a magnetic needle, and the field be varied either by varying the current or moving the magnet, a current will be developed in the conductor.  It is impossible at this distance to appreciate the interest excited by the announcement of this principle, not only among scientists, but also among inventors and those who saw practical possibilities for the future; and probably no one more fully appreciated its value than Faraday himself.  Yet he made no effort to develop it further, or even to protect his interest by a patent, as is common in these days.  He was eminently a scientist, and this was his free gift to the world.  He said:  “I have rather been desirous of discovering new facts and relations than of exalting those already obtained, being assured the latter would find their full development hereafter.”

Among the first to attempt successfully to exalt the new discovery was Pixii, an instrument maker of Paris, in 1832.  He wound two coils of very fine insulated wire upon the ends of a piece of soft iron, bent in a horseshoe form.  A permanent horseshoe magnet was then placed with poles very close to the ends of the iron in the coils.  The field so produced was then rapidly varied by revolving the magnet on an axis parallel to its length.  The soft iron cores of the coils became strongly magnetized as the poles of the revolving magnet came opposite to them; and their polarity was reversed at each half-revolution of the magnet.  By this plan currents of considerable intensity and alternating in direction at each revolution were induced in the coil.