hertz's researches on electrical waves. 



173 



tivity, but this could hardly be the case with «uch good insulators as 

 sulphur and paraffiue. Suppose moreover that the couductivity of the 

 di electric is sufficient to discharge the i^late JL in the ten-thousaudtb of 

 a second, but not much more rapidly. Then, during one oscillation, 

 the plates would lose only the ten-thousandth part of their charge, and 

 the conduction current in the substance experimented on would not ex- 

 ceed the ten-thousandth part of the primary current in A A', so that the 

 effect would be auite insensible. 



It was shown in the experiments described in the last section, that 

 when variable electrical for(;es act in the interior of di-electrics of specitic 

 inductive capacity not equal to unity, the corresponding electric dis- 

 l)lacemeuts produce electro-dynamic effects. In a paper "On the 

 Velocity of Propagation of Electro-Dynamic Actions," in Wiedemann's 

 AimaJen, lS8S,vol. xxxiv, p. 551, Dr. Hertz shows that similar actions take 

 place in the air, which proves, as was previously pointed out, that elec- 

 tro dynamic action must be i)ropagated with a finite velocity. 



The method of investigation was to excite electrical oscillations in a 

 rectilinear conductor in the same manner as in former experiments, and 

 then to produce effects in a secondary conductor by exciting electrical 

 oscillations iu it by means of those iu the rectilinear conductor, and at 

 the same time by the primary conductor acting through the intervening 

 space. This distance was gradually increased, when it was found that 

 the phase of the vibrations at a distance from the primary lagged behind 

 those in its immediate neighborhood, showing that the action is propa- 

 gated with a finite velocity, which was found to be greater than the 

 velocity of propagation of electrical waves in wires in the ratio of about 

 45 to 28, so that the former is of the same order as the velocity of light. 

 Dr. Uertz was unable to obtain any evidence with respect to the veloc- 

 ity of i»ropagation of electro-static actions. 



._2m 



Fic. 11. 



The primary conductor A A' (Fig. 11) consisted of a i)air of square 

 brass plates with sides 40 centinieters in length, connected by a copper 

 wire CO centimeters in length, at the middle point of which was an air 



