In the patent documents as well as in the earliest[11] articles in the journals concerning the system, two special forms of transformers are described, viz. that consisting of an iron core with the wire outside, and, secondly, that consisting of copper coils surrounded by iron wire. The transformers shown in Figs. 24 to 28 belong to the last of these classes, that in Fig. 23 to the first. The fundamental principle upon which all these transformers are constructed is that the subdivisions of the iron core run perpendicularly to the copper wires. Transformers such as are shown in Fig. 25 having a ring-shaped iron core wound with copper wire at first employed, later the inventors used in preference the form represented in Fig. 23.
In all these forms the principle is generally adhered to, that the magnetic resistance and the exciting power possess for each part of the length of the magnetic circuit the same value, and thus the formation of poles with the resulting dispersion of the lines of force is avoided.
This system procured for itself universal recognition, but especially in the Budapest Exhibition. There several exhibits within a radius of 1,300 metres were lit from a common central station. The several circuits were quite independent of one another, and lamps could be extinguished or lit in any one of them without anywhere producing a change in the intensity of the light, which could be perceived.
It was, therefore, in the year 1885 that the problem of current distribution by means of transformers was solved in a truly practical manner. The ideas which led the inventors to this thoroughly successful solution were then so unknown to practical and theoretical electricians, that it was long ere they were understood and appreciated. Even in February, 1886, such an electrician as Prof. Forbes maintained in his Cantor Lectures that the parallel connection of transformers was quite impracticable. He believed, namely, that a connection such as shown in Fig. 29 was useless, because the difference of potential at the generator diminished from the machine outwards, but that a connection such as shown in Fig. 30 must be used. According to him, in a direct system of distribution each lamp should have a separate lead, and having regard to the great number of leads which would thus be necessary, he concluded that the series method of connection was the right one. One would suppose that Prof. Forbes was not aware of the weighty disadvantages of this method. However, that was not the case. He proposed, that with series connection the strength of current should be kept constant, and that each transformer should have an especial regulating apparatus—the raising or lowering of the core; which, by the way, is an arrangement impracticable in a well designed transformer. Such a regulating apparatus has lately been made automatic.