182 hertz's researches on electrical waves. 



Table IV. 



From the results given in this table, the author draws the following 

 conclusions: 



(1) The interference does not change its sign at intervals of 2.8 meters. 

 The electro-dynamic actions are therefore not propagated with an infi- 

 nite velocity. 



(2) The interference is not in the same phase at all points, therefore 

 the electro-dynamic actions are not propagated through air with the 

 same velocity as electric waves in wires. 



(3) A gradual retardation of the waves in the wire has the effect of 

 displacing a given phase of the interference towards the origin of the 

 waves. The velocity of propagation through the air is therefore greater 

 than through a wire. 



(4) The sign of the interference is reversed at intervals of 7.5 meters, 

 and therefore in traversing this distance an electro-dynamic wave gains 

 one length of the waves in the wire. 



Thus, while the former travels 7.5 meters, the latter travels 7.5—2.8= 

 4.7 raeters, and therefore the ratio of the velocities is 75: 47, which gives 

 for the half- wave length of the electro-dyuamic action 2.8-f- 75/47 = 4.5 

 meters. Since this distance is traversed in 1.4/ hundred millionths of a 

 second, the absolute velocity of propagation through the air must be 

 320,000 kilometers per second. This result can only be considered re- 

 liable as far as its order is concerned; but its true value can hardly 

 exceed half as much again, or be less than two-thirds of this amount. 

 In order to obtain a more accurate determination of the true value it 

 will be necessary to determine the velocity of electric waves in wires 

 with greater exactness. 



It does not necessarily follow from the fact that in the immediate 

 neighborhood of the primary oscillation the interference changes its 

 sign after an interval of 2.8 meters that the velocity of propagation of 

 the electro-static action is infinite, for such a conclusion would rest upon 

 a single change of sign, which might moreover be explained independ- 

 ently of any change of phase, by a change in the sign of the amplitude 

 of the resultant force at a certain distance from the primary oscillation. 

 Quite independently however of any knowledge of the velocity of pro- 

 pagation of electrostatic actions, there exist definite proofs that the 

 rates of propagation of electro -static and electro-dynamic E. m. p.'s are 

 unequal. 



In the first place the total force does not vanish at any point on the 

 base-line. Now, near the primary, the electro-static e. m. f. is the greater, 



