1912] on High Frequenry Currents. 499 



necessary to supply the stator of tlie machine with an alternating 

 current. If it is excited with a direct current it will induce an 

 alternating current in the rotor which will react on the stator, and 

 backwards and forwards in the same way as I have already described. 



It would seem at first sight as if by this means an indetinitely high 

 frequency could be very easily obtained. There are, however, certain 

 practical difficulties. The actual connections used for a fourfold 

 magnetification of frequency are shown in Fig. 7. 



The stator S is excited from the battery B through the self-induc- 

 tion D. This produces in the rotor E an alternating current of the 

 frequency of say 100. This current flows through the condenser Cg, 

 the self-induction D.,, and the condenser C^. This circuit being in 

 resonance for 100 frequency, consequently the rotor behaves as if 

 short-circuited for this frequency. The iield produced Ijy this 100 

 frequency will react on the stator, and induce in it a current of 2(»0 

 frequency which passes via the condenser C^, self-induction D^, and 

 condenser Co. This circuit is also adjusted to be in resonance for the 

 frequency 2ik), and consequently the stator behaves as if short- 

 circuited for this frequency. There is in turn induced in the rotor 

 E a current of 300 frequency which passes via Cg and C^, again 

 adjusted to resonance. This induces in the stator a current of 400 

 frequency which, as circuit Dj C2 is not in resonance, for this frequency 

 can be taken out to do useful work from the points a and h. By 

 this method Dr. Goldschmidt has obtained some 12 "k.w. at a fre- 

 quency of 30,000, and at high freqtiencies a lesser output. Owing to 

 his courtesy I am able to show you some slides of the actual machine. 

 Fig. H is the rotor, and Fig. 9 the complete machine. 



The present position of the generation of high frequency currents 

 liy means of alternators may be resumed by saying that it is now 

 practically possible to generate by means of a machine alternating 

 current up to and over 200,000 frequency. At frequencies of 100,000 

 several k.w. are obtainable, and at the lower frequencies machines can 

 be built for greatly increased outputs. Where large amounts of power 

 at high frequencies are required such as in wireless telegraphy, the 

 question is now becoming a commercial one as to the efficiency of the 

 different types of alternator, their cost and their reliability. Is it 

 possible to run these machines continuously day in day out and to 

 supply power at high frequencies ? If so, how much does it cost per 

 kilowatt hour to produce this high frequency power, taking into 

 account not only the coal consumption, but also the wear and tear on 

 the machine and all the other running and capital charges ? 



Leyden Jar Discharges. 



Turning next to the second method of producing high frequency 

 currents— namely, by the discharge of a Leyden jar — it was quite early 

 inferred by Helmholtz and Henry that the discharge of a Levden jar 



Vol. XX. (No. 106) 2 l 



