152 hertz's eese arches on electrical waves. 



iiig the knobs of the discharger B apart until sparks ceased to pass 

 showing that the effect was not due to the electro-static potential differ 

 ence of C C, as this would be increased by separating the discharger 

 knobs beyond sparking distance. 



The closed micrometer circuit was then replaced by a straight copper 

 wire, slightly shorter than the distance C C, placed parallel to C B C", 

 and at a distance of 60 centimeters from it. This wire terminated in 

 knobs, 10 centimeters in diameter, attached to insulating supports, and 

 the spark micrometer divided it into two equal parts. Under these cir- 

 cumstances sparks were obtained at the micrometer as before. 



With the rectilinear open micrometer circuit sparks were still observed 

 at the micrometer when the discharger knobs of the secondary coil cir- 

 cuit were separated beyond sparking distance. This was of course due 

 simply to electro- static induction, and shows that the oscillatory current 

 in G C was superposed upon the ordinary discharges. The electro-static 

 action could be got rid of by joining the micrometer knobs by means of 

 a damp thread. The conductivity of this thread was therefore sufficient 

 to afford a passage to the comparatively slow alternations of the coil 

 discharge, but was not sufficient to provide a passage for the immeas- 

 ureably more rapid alternations of the oscillatory current. Considerable 

 sparking took place at the micrometer when its distance from G B C 

 was 1 or 2 meters, and faint sparks were distinguishable up to 3 meters. 

 At these distances it was not necessary to use the damp thread to get 

 rid of the electro-static action, as owing to its diminishing more rapidly 

 with increase of distance than the effect of the current induction, it was 

 no longer able to produce sparks in the micrometer, as was proved by 

 separating the discharger knobs beyond speaking distance, when sparks 

 could no longer be perceived at the micrometer. 



Resonance 'phenomena. — In order to determine whether, as some minor 

 phenomena had led the author to suppose, the oscillations were of the 

 nature of a regular vibration, he availed himself of the principle of reso- 

 nance. According to this principle, an oscillatory current of definite 

 period would, other conditions being the same, exert a much greater in- 

 ductive effect upon one of equal period than upon one differing even 

 slightly from it.* 



If then two circuits are taken, having as nearly as possible equal 

 vibration periods, the effect of one upon the other will be diminished by 

 altering either the capacity or the coefficient of self-induction of one of 

 them, as a change in either of them would alter the period of vibration 

 of the circuit. 



This was carried out by means of an arrangement very similar to that 

 of Fig. 4. The conductor G G' was replaced by a straight copper wire 

 2.6 meters in length and 5 millimeters in diameter, divided into two equal 

 parts, as before, by a discharger. The discharger knobs were attached 



See Oberbeck, Wiedemann's Annalen, 1885, vol.xxvi, p. 245. 



