Nikola Tesla Books
195 THE CONSTRUCTION OF LARGE APPARATUS of the transformer is so designed that a consumption of current varying from 2 to 4 k.w. may be obtained. The Spark Gap.-The apparatus previously described is designed for use with a rotary spark gap. Reference to Fig. 9 will disclose the fact that the spark gap is of simple construction and that it consists essentially of a disc of ½-inch aluminum, carrying 12 discharge points or studs of nickel steel, mounted upon the shaft of a small alternating current motor and surrounded by a housing of wood which serves the double purpose of a muffler to deaden the noise of the spark discharge and a support to carry the stationary electrodes E in Fig. 9. This drawing represents a side elevation of the complete gap shown partly in cross section in order that the relative positions of motor, rotary disc and stationary electrodes may be shown. Fig. 10 shows an end elevation of the gap housing and it also serves to indicate the position of the stationary electrodes. Attention should first be directed to the rotor of the gap. This should be laid out on a piece of ½-inch sheet aluminum rather more than 10 inches square. After finding the center, a circle with a diameter of 10 inches is inscribed upon the aluminum and then a 9-inch diameter circle is laid out and finally one of 3-inch diameter. The sheet of aluminum is then mounted upon a wooden faceplate in the lathe and a cut taken quite through the metal on the line of the smallest circle, thus leaving an opening 3 inches in diameter when the disc of metal is removed. A similar cut is taken on the largest circle resulting in the rotor disc which is now ready to be mounted upon the insulating hub of fibre, indicated at C, in Fig. 11, which gives an elevation and section of the rotor disc complete. The insulating hub is turned up from a piece ¾½-inch sheet fibre to the dimension given in the enlarged drawing. Fig. 12. The reader will note that the fibre hub is mounted
