CHAPTER XXX.

Alternate Current Electrostatic Induction Apparatus . 1

About a year and a half ago while engaged in the study ofalternate currents of short period, it occurred to me that suchcurrents could he obtained by rotating charged surfaces in closeproximity to conductors. Accordingly I devised various forms

Fig. 208.

of experimental apparatus of which two are illustrated in theaccompanying engravings.

In the apparatus shown in Fig. 208, a is a ring of dry shel-lacked hard wood provided on its inside with two sets of tin-foilcoatings, a and b, all the a coatings and all the b coatings beingconnected together, respectively, but independent' from eachother. These two sets of coatings are connected to two termi-

1. Article by Mr. Tesla in The Electrical Engineer, N. Y., May 6, 1891.