E 



462 The Direction of Force and Acceleration. 



four field equations, for the ease of a moving point charge, — 



= \ 1 -7*)—r^ \j- • • • (b) 



^ 6/ R3^l_^ s in^y 



H=-vxE, (7) 



c 



where R is the radius vector connecting the moving charge 

 with the point in question and i/r is the angle between R 

 and v. 



For the field acting on the test electron t, situated at the 

 point .x = Q } y—y, we may substitute R=^/j and sin^r = l, 

 giving us, 



and 



// 



>-*/ 



substituting into the fifth fundamental equation of electro- 

 magnetic theory, 



F = E+ 1 vxH (10) 



c 



we obtain the force acting on the unit test electron t. 



[Note in the above equation that v, the velocity of the 

 electron, is for our case ri + %j.] 



P 7'?/ 



F*= , , A1 ^ (12) 



,2/ 



^=-7-^(1- J).- • • • (1 



Under the action of the component force F z we might at 

 first sight expect the electron t to aqnire an acceleration in 

 the X direction. Such a condition, however, would not be 



in agreement with the principle of relativity, since from the 



