HIGH FREQUENCY AND HIGH POTENTIAL CURRENTS. 393

nals, t. For tlie sake of clearness only a few coatings are shown.Inside of the ring a, and in close proximity to it there is arrangedto rotate a cylinder b, likewise of dry, shellacked hard wood, andprovided with two similar sets of coatings, a x and b x , all the coat-ings a 1 being connected to one ring and all the others, ¥, toanother marked + and —. These two sets, a x and b x are chargedto a high potential by a Holtz or Wimsliurst machine, and maybe connected to a jar of some capacity. The inside of ring a iscoated with mica in order to increase the induction and also toallow higher potentials to be used.

When the cylinder b with the charged coatings is rotated, a

Fin. 2(H).

circuit connected to the terminals x is traversed by alternatingcurrents. Another form of apparatus is illustrated in Fig. 209.In this apparatus the two sets of tin-foil coatings are glired on aplate of ebonite, and a similar plate which is rotated, and thecoatings of which are charged as in Fig. 208, is provided.

The output of such an apparatus is very small, but some oftlie effects peculiar to alternating currents of short periods maybe observed. The effects, however, cannot be compared withthose obtainable with an induction coil which is operated by analternate current machine of high frequency, some of whichw T ere described by me a short while ago.