506 Mr. W. Duddell on High Frpqiienry Currents. [May 17, 1912 



completely joined up, and the result almost the same as if an alter- 

 nator were employed. 



Mr. Galletti informs me that he has been able to employ still 

 larger numbers of sparks per second, up to 100,00(i. In this case 

 one arrives at the interesting result that the oscillations can be 

 maintained by impulses from the condenser circuit every other 

 oscillation, or even each individual oscillation. This should maintain 

 a true alternating current, such as is produced by an alternator, with 

 no waste intervals. 



To experimentally illustrate the principle, I have arranged two 

 circuits according to Mr. Galletti's method. As I have not at my 

 disposal a very high voltage — in fact, I have only 90(3 volts — I am 

 using vacuum tubes T^ T., in place of the spark gaps, as by adjusting 

 the pressure I can make them discharge regularly at these low- 

 voltages. 



In order to demonstrate that the two circuits I am using really 

 discharge in regular sequence and not simultaneously, I am using a 

 low discharge frequency of about 1 per second. This is obtained 

 by giving t!ie condensers 0^ C^ (J., each a capacity of abont 5 mf., 

 aint using 100,000 ohms for R;^ and R., in series in each circuit. 

 By short-circuiting the common condenser C,, the sequence of suc- 

 cessive discharges is at once destroyed, and the condensers of the 

 two circuits tend to discharge simultaneously. When I reduce the 

 series resistances the discharge rate is greatly increased, until it is no 

 longer possible by eye or eai- to realize the frequency. I have, by 

 experiments with the oscillograph, determined that the discharges 

 still take place in regular sequence. 



Aec Methods. 



I now come to the third method — namely, the arc method of 

 producing high frequency currents. If an ordinary direct current 

 arc is produced between solid carbon or metal electrodes, it is 

 unstable —that is to say, it cannot be burnt unless a resistance is 

 placed in series Avith it. The reason for this will be at once evident 

 if we examine the curves in Fig 12, connecting the potential difference 

 and the current. It will be noted that if the current through the 

 arc is increased, due to any cause, the potential difference l)etween 

 its terminals decreases. The result of this decrease in potential 

 difference is to encourage a still larger current to flow. This larger 

 current further decreases the potential difference, and, consequently, 

 still further increases the current, the current tending, therefore, to 

 become infinitely great. If, on the other hand, the current be 

 decreased, the potential difference between the terminals of the arc 

 tends to increase, which has the result of tending to still further 

 decrease the current, causing the current to become zero, so that an 



