Charging Device for Electroscope

Abstract

Those who have used an ebonite rod or a miniature static machine to charge an electroscope during wet weather realize that it leaves much to be desired. The step-up transformer operated on A.C. and using a vacuum tube rectifier is more satisfactory, but is complicated and expensive. For the past six months the author has been using a simple and inexpensive arrangement composed of a Ford spark coil operated on two or three dry cells. This gives a high voltage direct current whose positive pole is connected to a fine needle point placed about three-quarters of an inch from the post that supports the leaf. This distance is much greater than the actual sparking distance of the coil, but allows a gentle brush discharge to take place, slowly lifting the leaf to the desired potential. By being lifted slowly (two or three seconds) the leaf is spared any sudden jerk, which might result in damage. No switching device is needed except a push button in the primary circuit. The accompanying photograph and drawing (Fig...