146 hertz's researches on electrical waves. 



According to these iiivestigatious, the electrical oscillations produced 

 in an open circuit by means of an induction coil are measured by ten 

 thousandths of a second, while in the case of the oscillatory discharge 

 of a Leyden jar they are about a hundred times as rapid, as was shown 

 by Feddersen. 



According to theory, still more rapid oscillations should be possible 

 in an open circuit of wire of good conducting material, provided its ends 

 are not connected with conductors of any considerable capacity ; but it 

 is not possible to <letermine from theory whether measurable oscilla- 

 tions are actually produced. Some observations of Hertz's led him to 

 believe that under certain circumstances oscillations of this kind were 

 ])roduced, and his researches show that this is so, and that the oscilla- 

 tions are about a hundred times as rapid as those observed by Fedder- 

 sen; so that their periods are measured by hundred millionths of a 

 second, and they therefore occupy a position intermediate between 

 acoustic and luminous vibrations. 



Preliminary Uxpcriments. — It is known that if in the secondary circuit 

 of an induction coil there be inserted, in addition to the ordinary air 

 space, across which sparks pass, a Riess spark micrometer, with its 

 poles joined by a long wire, the discharge will pass across the air space 

 of the micrometer in preference to following the path of least resistance 

 through the wire, provided this air space does not exceed a certain 

 limit, and it is upon this principle that lightning protectors for tele- 

 graph lines are constructed. It might be expected that the sparks 

 could he made to disappear by diminishing the length and resistance 

 of the connecting wire; but Hertz finds that though the length of the 

 sparks can be diminished in this way, it is almost impossible to get rid 

 of them entirely, and they can still be observed when the balls of the 

 micrometer are connected by a thick copper wire only a few centimeters 

 in length. 



This shows that there must be variations in the potential measure- 

 able in hundredths of a volt in a portion of the circuit only a few centi- 

 meters in length, and it also gives an indirect proof of the enormous 

 rapidity of the discharge, for the difference of potential between the 

 micrometer knobs can only be due to self-induction in the connecting 

 wire. Now the time occupied by variations in the potential of one of 

 the knobs must be of the same order as that in which these variations 

 can be transmitted through a short length of a good conductor to the 

 second knob. The resistance of the wire connecting the knobs is found 

 to be without sensible effect on the results. 



L. Lorenz, Wiedemann's Avnalen, 1879, voL A'li, page 161. 



Olearsky, Verhaudlnngen der Academic von Krakau, 1882, vol. vii, page 141. 



Kolacek, Beibliitter zu Wiedemann's ^nwa/oj, 1883, vol. vii, page 541 (abstractor 

 a paper published in the reports of the Bohemian Scientific Society in 1882). 



Bichat et Blondlot, Comptes liendus, 1882, vol. xciv, page 1590. 



Oberbeck, Wiedemann's Annakn, 1882, vol. xvii, ])ages SIG and 1040; 1883, vol, 

 XIX, pages 213 and 265. 



