ELECTRIC OSCILLATIONS AND ELECTRIC WAVES. 261 



electrical stress. The explanation here given of the entire relief 

 of the electrical stress between two plates by the establishment 

 of a conducting line (line of slip) between them applies to two 

 adjacent oppositely charged bodies of any shape. An electric 

 spark is a line o/ slip (a conducting line), and the energy of the 

 electric field flows in upon the spark as it does upon a wire. The 

 slipping of ether cells in a conductor is imagined to be opposed 

 by a frictional drag. 



Fig. 204. 



The Hertz oscillator. Let A and B, Fig. 204, be two metal 

 balls connected to two short rods between which is an air gap 

 (spark gap) . Imagine charge to have been collecting on A and 

 B, positive charge on A, negative charge on B, until a spark 

 jumps across the air gap, thus establishing a conducting path 

 from A to B, and causing A and B to be discharged. This 

 discharge is usually oscillatory like the movement of a string 

 which is pulled to one side and suddenly released. Con- 

 sider a chain of geared ether cells which, when undistorted, 

 lies smoothly along the dotted line in Fig. 204, this dotted line 

 being everywhere perpendicular to the lines of force of the 

 electric field. When A is positively charged, this chain is 



