HERTZIAN WAVE ]YIHELESS TELEGRAPHY. 371 



also to Professor Braim. In this case, a condenser and inductance are 

 connected in series to the spark balls of an induction coil, and oscilla- 

 tions are set up in this circuit. Accordingly, there are rapid fluctuations 

 of potential at one terminal of the condenser. If to this we connect a 

 long aerial, the length of which has been adjusted to be one quarter 

 of the length of wave corresponding to the frequency, in other words, 

 to make it a quarter wave resonator, then powerful oscillations will be 

 accumulated in this rod. The relation between the height (H) of the 

 aerial and the frequency, is given by the equation 3 X 10" = 4:7iH, 

 where n is the frequency of the oscillations and H the height of the 

 aerial in centimeters. The frequency of the oscillations is determined 

 by the capacity (C) and inductance (L) of the condenser circuit, and 

 can be calculated from the formula 



5,000,000 



V C (in mfds. ) X L {in cms. ) 



That is, the frequency is obtained by dividing into the number 5,000,- 

 000, the square root of the product of the capacity in microfarads, and 

 inductance in centimeters, of the condenser circuit. It will be found, 

 on applying these rules, that it is impossible to unite together any 

 aerial of a length obtainable in practise with a condenser circuit of 

 more than a very moderate capacity. It has-been shown that for an 

 aerial two hundred feet in height the corresponding resonating fre- 

 quency is about one and a quarter million.* As we are limited in 

 the amount to which we can reduce the inductance of a discharge 

 circuit, probably to something like a thousand centimeters, a simple 

 calculation shows that the largest capacity we can employ is about 

 a sixtieth of a microfarad. This capacity, even if charged at 60,000 

 volts, would only contain thirty joules of energj^, or about 22.5 foot- 

 pounds, which is a small storage compared to that which can be 

 achieved when we are employing the above described methods, which 

 involve the use of an oscillation transformer. In such a case, how- 

 ever, it is an advantage to employ a spark gap in compressed air, 

 because we can then raise the voltage to a much higher value than in 

 air of ordinary pressure without lengthening the spark so much as 

 to render it non-oscillatory. 



When employing methods involving the use of an oscillation trans- 

 former, it is possible to use multiple aerials having large capacity, and 

 hence to store up a very large amount of energy in the aerial, which 

 is liberated at each discharge. The most efEective arrangement is one 



* That this number really does represent the order of this oscillation fre- 

 quency in an aerial has been shown by C. Tissot, Comptes Rendus, 132, p. 763, 

 March 25, 1901, by photographs taken of the oscillatory spark of a Hertzian 

 wave telegraphic transmitter. (See Science Abstracts, Vol. IV., Abs. 1518.) 

 He found frequencies from 0.5 million to 1.6 million. 



