HERTZIAN ^yAVE WIRELESS TELEGRAFUY. 



117 



impulses, the time period of which depends iipon the capacity of the 

 jar and the inductance of the discharge circuit. We can, moreover, 

 vary this frequency over wide limits. Parallel to the long spiral wire 

 is suspended another copper wire E (see Fig. 10), and between this 

 wire and the silk-covered copper wire dis- 

 charges take place due to the potential differ- 

 ence between each part of the wire and this 

 long aerial wire. If we arrange matters so 

 that the impulses communicated to the bottom 

 end of the long spiral wire correspond to its 

 fundamental note or periodic time, then in 

 a darkened room we shall see a luminous glow 

 or discharge between the vertical wire and the 

 spiral wire, which increases in intensity all 

 the way up to the top of the spiral wire. The 

 luminosity of this brush discharge at any f^g. 10. seibt-s apparatus 



° FOR SHOWING STATIONARY 



point is evidence of the potential of the spiral waves in long solenoid a. 

 wire at that point, and its distribution clearly ^. Eduction coii ;^. spark gap 



^ ' •' i, inductance coil; C1C2, Ley- 



demonstrates that the difference of potential den jars ; ^, earth wire, 

 between the spiral wire and the aerial increases 



all the way up from the bottom to the top of the spiral wire. In the 

 next place, by making a little adjustment and by varying the induct- 

 ance of the jar circuit, we can increase the frequency of the impulses 

 which are falling upon the spiral wire; and then it will be noticed 

 that the distribution of the brush discharge or luminosity is altered, 



and that there is a maximum now at about 

 one third of the height of the spiral wire, 

 and a dark place at about two thirds of the 

 height, and another bright place at the top, 

 thus showing that we have a node of poten- 

 tial at about two thirds the way up the wire 

 (see Fig. 11), and we have therefore set 

 up in the spiral wire electrical oscillations 

 corresponding to the first overtone. It is 

 possible to show in the same way the exist- 

 ence of the second harmonic in the coil, but 

 the luminosity then becomes too faint to 

 be seen at a distance. 



An interesting form of aerial devised by 

 Professor Slaby, of Berlin, depends for its action entirely on the fact 



that the electrical oscillations set up in it which radiate are harmonics 

 of the fundamental tone. 



Fig. 11. Harmonic Oscilla 

 TioNS IN Long Solenoid shown 

 with Seibt's Apparatus. 



