ELECTRIC OSCILLATIONS AND ELECTRIC WAVES. 263 



cells are all in uniform rotation as indicated by the small curved 

 arrows, and within the region of the wave the chains of cells are 

 all distorted, positive cells being displaced upwards with respect 

 to the negative cells, as shown in Fig. 195. 



electric current 



Throughout the middle portion of the wave each rotating cell 

 is acted upon by equal and opposite torques by the adjacent cells 

 ahead of it and behind it, as explained in connection with Fig. 

 175.* Therefore all the cells in the middle portion of the wave 

 continue to rotate at unchanging speed, and the zigzag distortion 

 of the chain of cells remains unchanged in the middle portion of 

 the wave The cell d, however, exerts an unbalanced torque 

 upon the cell f, as indicated by the dotted arrow T f , and this 

 torque quickly sets the cell f into rotation. Also the cell b 

 exerts an unbalanced torque T upon the cell c which quickly 

 stops the rotation of the cell c. Thus the combinea state of 

 motion and distortion of the ether cells between c and f travels 

 to the right. 



The terminating of the electric lines of force on the wires (or 

 metal sheets) which bound the electric wave constitutes electric 



* Figure 195 represents what may be called a rectangular electromagnetic wave 

 pulse throughout which the electric field is uniform and throughout which the mag- 

 netic field is uniform. 



