Now the magnetic resistance of a symmetrical iron ring is constant in all parts of the length of its magnetic circuit. In the case in question only one half of the ring was excited, therefore poles must have been formed at both ends of the exciting coil. The ratio of transformation of this apparatus of Faraday’s was equal to unity, so it had therefore no claim to the designation of “transformer.” The induction apparatus of Faraday in its simplicity was in a certain measure the embryo out of which all dynamos and transformers have developed. We have seen how the first induction current was discovered by making and breaking the current from a battery in the primary coil. This method was at first adhered to, until Faraday remarked that when the secondary was quickly drawn out of or put into the primary coil, induced currents were also produced without requiring to break the circuit, the wires of the secondary coil cutting the lines of force in the magnetic field of the primary coil. He then replaced the primary coil and battery by a permanent magnet, which was likewise dipped into the induction coil, Fig. 3. [Illustration: FIG. 3.] [Sidenote: Henry and Page, 1836.] From this, and from the later development of this invention, it follows that the question was not of a transformer in the present sense of the word, but of a secondary generator. Transformers as at present understood were first known in Europe as the Ruhmkorff’s induction coil. Before we take up this invention we shall mention a much earlier and like invention, which had already been made in the United States in the year 1838. This was the induction coil of Professor Page, and was the outcome of another invention by Professor Henry, whose apparatus was only a single induction coil. The first public notice of Professor Page’s apparatus appeared in the Silliman-Journal of 12th May, 1836, under the title, “Methods and trials of obtaining physiological phenomena and sparks from a heat engine by means of Professor Henry’s apparatus.” In May, 1837, Sturgeon published, in the “Annals of Electricity,” in London, a description of the apparatus of Henry and Page. [Sidenote: Callan, 1837.] Callan, an English student of physics in Minnoth, showed first, in the year 1837, that if high tension was wanted, it was necessary to employ thick wire for the primary and thin for the secondary coil. Before this time wires indeed of different lengths, but of equal cross sections, had always been employed. His apparatus was not so bad as those before known, but still stood far behind that of Professor Page. [Sidenote: Page, 1838.]