LATEST DF.VELOPMENT& WITH THE X RAYS. 663 



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 produeinj^ electrical sparks six feet in length. 



A fourth method, first used by Professors Xorton and Goodwin, 

 •of the Massachusetts Institute of Technology, consists in discharg- 

 ing 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 elec- 

 tricity than have been hitherto used. The accompanying photo- 

 graph 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 



