168 hertz's researches on electrical waves. 



conductor close to the opposed surfaces of the spheres forming the ter- 

 minals at the primary air space, even when no visible sparking- took 

 jdace between the latter and the insulated conductor. The secondary 

 sparking could also be stopped by placing a fine point close to the pri- 

 mary air space, or by touching one of the opposed surfaces of the ter- 

 minals with a pie^e of sealing wax, glass, or mica. Dr. Hertz states 

 that further experiments have led him to conclude that even in these 

 cases the effect is due to light too feeble to be perceived by the eye, 

 arising from a side discharge. He points out that these effects afford 

 another example of the effects of light on electric discharges, which 

 have been observed by E. Wiedemann, H. Ebert, and W. Hallwachs. 



\ 



Dr. Hertz's next paper in order of publication in Wiedemann's A^ina- 

 len, "On Some Induction Phenomena Arising from Electrical Actions in 

 Dielectrics" (Wiedemann's Amialen, 1888, vol. xxxiv., p. 273), contains 

 an account of some researches undertaken with a view of obtaining direct 

 experimental confiruiatiou of the assumption involved in the most sug- 

 gestive theory of electrical actions, viz, that of Faraday and Maxwell, 

 that the well-known electro-static phenomena observed in dielectrics are 

 accompanied by corresponding electro-dynamic actions. The method 

 of observation consisted in placing a secondary conductor adjusted to 

 unison, as regards electrical oscillations, with the primary, as near as 

 possible to the former, and in such a relative position that the sparks 

 in the primary produced no sparking in the secondaiy. As the equilib- 

 rium could be disturbed and sparking induced in the secondary by the 

 approach of conductors, it formed a kind of induction balance; but the 

 point of special interest in connection with it was that a similar effect 

 was produced when the conductors were replaced by insulators, pro- 

 vided the latter were of comparatively large size. The observed rapidity 

 of the oscillations induced in the di-electrics showed that the quantities 

 of electricity in motion under the influence of di-electric i)olarization 

 were of the same order of magnitude as in the case of metallic conduct- 

 ors. 



The apparatus employed is shown diagrammatically in Fig. 10, and 

 was supported on a light wooden framework, not shown in the illustra- 

 tion. The primary conductor consisted of two brass plates, AA', with 

 sides 40 centimeters in length, joined by a copper wire 70 centimeters 

 long and half a centimeter in diameter, containing an air space of three- 

 quarters of a centimeter, with terminals formed of ])0'.ished brass spheres. 

 When placed in connection with a powerful induction coil, oscillations 

 are set up, the period of which, determined by the dimensions of the 

 primary, can be determined to a hundred millionth of a second. The 

 secondary conductor consisted of a circle, 35 centimeters in radius, of 

 copper wire 2 millimeters in diameter, containing an air space, th'> 



