run at a high rate of speed. Both of these methods have their advocates. The use of the Ruhmkorf coil is the most universal.
The third method consists in charging a number of Leyden jars by a storage battery and in discharging these one after another, so as to obtain a high electro-motive force. This method is a very flexible one. I can experiment with my apparatus over a range of electric pressure extending from twenty thousand units to three million. The electrical discharge produced by three million units or volts is over six feet in length.
The apparatus for discharging the Leyden jars or condensers in series is represented in Fig. 2.
Fig. 2.—Apparatus for producing electrical sparks six feet in length.
A fourth method, first used by Professors Norton and Goodwin, of the Massachusetts Institute of Technology, consists in discharging a quantity of electricity through the coarse coil of a Ruhmkorf coil. This method obviates the necessity of a mechanical break to interrupt the battery current which is employed to excite the current in the coarse coil of this apparatus.
I have experimented with more powerful quantities of electricity than have been hitherto used. The accompanying photograph gives an idea of the magnitude of the quantity which I can use to excite the X rays.
It represents the discharge, burning a fine iron wire, and it
