Page:Collected Physical Papers.djvu/23

Rh Radiator.—Electric oscillation is produced by sparking between hollow hemispheres, and a small interposed sphere. The two beads attached to the hemispheres and	the interposed sphere were at first thickly coated with gold, and the surface highly polished. This worked satisfactorily for a time, but after long-continued action, the surface of the ball became roughened and the discharge ceased to be oscillatory. After some difficulty in obtaining the requisite high temperature, I succeeded in casting a solid ball and two beads of platinum. There is now no difficulty in obtaining an oscillatory discharge; the sparks are made very small, as these are more effective with the receiver used. After a little experience, it is possible to tell whether the discharge is oscillatory or not. The effective sparks have a peculiar smooth sound, whereas non-oscillatory discharges give rise to peculiar cracked sound.

As an electric generator, I at first used a small Ruhmkorff coil actuated by a battery. I, however, soon found that the usual vibrating arrangement is a source of trouble; the contact points soon get worn out, and the break becomes irregular. The oscillation produced by a single break is quite sufficient for a single experiment, and it is mere waste to have a series of useless oscillations. But the most serious objection to the production of secondary sparks, unless absolutely wanted, is their deteriorating action on the spark balls.