Nikola Tesla Books
CHAPTER XIV. NOTES FOR THE BEGINNER IN ELECTROTHERAPEUTICS. This chapter is intended, as its name implies, for the physician who feels a growing interest in the possibilities of electro-therapeutics but who knows very little of the subject. The discussion, therefore, opens with a description of the electrical apparatus in order that the lay reader may understand the reference to the various instruments in the latter portion of the chapter. The Transformer.-The alternating current taken from the house lighting circuit at perhaps 110 volts is passed through a suitable controlling switch to the primary of the transformer. The function of this device is to change the iÅtensity or voltage of the current from that suitable for lighting lamps to one many hundred times higher. The principle of the transformer has already been discussed in these columns, but for the benefit of the lay reader it may be said to be briefly as follows: When an alternating current is made to flow through a wire, a similar current will be produced in a second wire placed beside the first but having no connection with it. If the two wires be wound into coils and the coils placed side by side, the effect is greatly enhanced, and if a mass of laminated iron be placed within the openings in the coils the effect shows a very marked increase. This property of the alternating current is known as "induction" and the current produced in the second wire is said to be induced by that in the first. The 137
