6 C. A. Chard— Variation of Potential along the 



In all the curves abscissas represent distances from the free 

 end and ordinates magnetometer deflections. 



It is seen from the curves, that joining to earth one pole of the 

 oscillator is equivalent to adding to that pole a wire similar to 

 the antenna ; or, in other words, the earth acts like a plane 

 mirror in optics. This view has been put forward by several 

 writers, especially by Slaby* when offering an explanation of his 

 system of syntonic telegraphy. 



In the curve obtained with the antenna of 1000 cms connected 

 to earth (see fig. 3), there is a deep minimum at approximately 

 123 cms from the free end, and a second one at 375 cms . This 

 would give 



A/2 = 2X123 = 246 cms 

 = 375 — 123 = 252 cms 



Mean 249 cms 



In the curve obtained with no earth or other connection the 

 natural oscillation of the wire as a whole is practically absent, 

 but there are minima at distances 



130, 425, 725, (1000?) cms 



That at 1000 cms is not decisive from the curve, and so it is 

 omitted in the following calculation ( though including it would 

 make no difference in the result) : 



A/2 = 2X130 = 260 cms 

 = 425 — 130 ==. 295 cms 

 — lib— 425 = 290 cms 



Mean 282 cms 



These, I believe, are half-wave-lengths of overtones. In the 

 first case the wire was grounded and so only odd overtones 

 would be possible, the one present being probably the ninth, 

 counting the fundamental, the first. If such was the case, the 

 entire length of the oscillating wire from free end to earth 

 should be 



249 



9X — = 1120 cms , 



a result requiring the oscillator to be equivalent to 



1120 — (1000 + 75), or 145 cms 



of the wire. This value appears rather high, but this explana- 

 tion seems to me the most probable. 



I may remark that the curves obtained with the wire 

 1000 cms long, connected to the earth, were the most irregular of 



* A. Slaby, Funkentelegraphie, 2d ed., p. 86, and fol. Berlin, 1901. 



