ELECTRIC OSCILLATIONS AND ELECTRIC WAVES. 257 



Therefore, we have in general 



I 



47T 



(I) 



in which S is the energy in ergs per second which streams across 

 one square centimeter of area at right angles to a magnetic field 

 of which the intensity is M gausses and at right angles to an 

 electric field of which the intensity is e ab volts per centimeter, 

 &C and e being at right angles to each other. 



(b) The flow of energy in the neighborhood of wires assumed to 

 be of zero resistance. In this case the component of the electric 

 field parallel to the surface of the wires is equal 

 to zero, and the only electric field which exists, 

 if any, is that which is associated with charges 

 on the surfaces of the wires or ribbons. An 

 ideally simple case is shown in Fig. 199, in 

 which A A and BB are straight wires (rib- 

 bons), assumed to be of zero resistance, which 

 deliver current from a voltaic cell to a fine resist- 

 ance wire (ribbon) w. The electric field between 

 the ribbons A A and BB is uniform, and 

 the lines of force of the electric field are repre- 

 sented by the fine horizontal lines in the figure; 

 the intensity of the electric field is equal to the 

 electromotive force of the voltaic cell divided by 

 the distance between the ribbons. The mag- 

 netic field between the ribbons is uniform, and 

 the lines of force of the magnetic field are per- 

 pendicular to the plane of the paper in Fig. 199 

 as indicated by the dots between A A and 

 BB. The energy stream, being everywhere at right angles to 

 the electric and magnetic fields, is straight upwards as indicated 

 by the dotted arrows. If the wires (ribbons) in Fig. 199 have re- 

 sistance, then the lines of force of the electric field turn slightly 

 downwards (in the figure) near each ribbon on account of the RI 

 18 



199. 



