He followed the principle of making each secondary circuit and each point of consumption independent. The means to this purpose which he thought to employ were not practical, and did not at all differ in substance from those of his predecessors. His system is remarkable for his method of connecting the induction coils in the main lead, i.e. in series, using the secondary currents from these coils to excite other coils from which tertiary currents were received, and these again were further used to excite quaternary currents, and so on. This procedure stands on a level with that of the famed dynamo-electric chain of Siemens and Halske, of which it has been asked, “To what purpose?” The peculiarities of the system of Haitzema Enuma become evident from the following extract from his patent:— “Solche (nämlich die bekaunten) Induktionsrollen werden in den Hauptstromkreis überall eingeschaltet, wo der Strom abgezweigt (!) werden soll; und durch diese Einrichtung erhält zuletzt jede elektrische Lampe, oder jeder durch Elektrizität in Betrieb gesetzte Apparat seinen eigenen Strom.” Haitzema Enuma had intended, so far as this shows, to connect the primary, secondary, tertiary, &c., coils in series, and the main lead being a closed circuit, the ends were taken to earth. The ends of the circuits of the secondary, tertiary, and further induced currents, were also connected together, or to earth. [Sidenote: Gaulard and Gibbs, 1883.] The first who came forward with an industrial employment of the series system were Gaulard and Gibbs, who, in the year 1883, placed before the public an installation of electric lighting in the Royal Aquarium in London. [Illustration: FIG. 18.] There were two such apparatus as shown in Fig. 18, which were connected in series, and excited with 13 ampères from a Siemens’ alternating current dynamo. The apparatus had the following construction:—The induction coils, a section of one of which is shown in Fig. 19, had three layers of primary wire, and the secondary was wound in four divisions, the ends of the wires of the divisions being led to a commutator. Fig. 20 shows this commutator placed in the middle of four induction coils. The ends of the secondary wires were connected to eight terminals on the upper plate of the apparatus, from which the current could be led away from each pair, or combined at will. By aid of the commutator, the number of coils in circuit could be altered as desired. On the lower plate there was a second commutator, which served the same purpose for the primary circuit. [Illustration: FIG. 19.] The core of the apparatus consisted of bars of insulated iron, and by means of a rack could be raised or lowered in the coils for the regulation of the current. Both of these arrangements had been already long known. In the same year another installation for the lighting of some stations on the Metropolitan Railway was taken in hand and carried out. [Illustration: FIG. 20.]