THE WORLD'S ADVANCE 



125 



lations in the circuits, even when the two 

 are separately tuned to the same fre- 

 quency, are not simple damped oscilla- 

 tions, but can be analyzed into a complex 

 vibration of two different frequencies.* 

 These two oscillations have different 

 damping factors and the total energy is 

 distributed, not equally, between the two. 

 When the second of the coupled circuits 

 is an antenna this complex oscillation is 

 undesirable and the usual procedure has 

 been to weaken the coupling between the 

 antenna and the exciting circuit, which 

 has the effect of confining the greater 

 part of the energy transferred to one of 

 the oscillations at the expense of the 

 other. While this results in better defi- 

 nition of the radiation as regards single- 

 ness and sharpness of wave, there is a 

 considerable loss in efficiency due to 

 loose coupling. An arrangement where- 

 by tight coupling with high efficiency at 

 the oscillation transformer can be util- 

 ized and still maintain single wave radi- 

 ation is much to be desired. 



The success of such an arrangement 

 depends on the use of a suitable spark 

 gap. The parallel plate quenched gap 

 is an excellent example of what can be 

 done in this direction. With such a gap, 

 properly adjusted, oscillations in the 

 closed circuit are highly damped, as 

 shown by Fig. i, and these induce pow- 

 erful free oscillations in the antenna of 

 single frequency and the damping of 

 which is determined only by the con- 

 stants of the antenna. (See Fig. 2.) 

 Very close coupling can be used without 

 the appearance of a complex oscillation, 

 because return of energy from the an- 

 tenna to the closed circuit is prevented 

 by the automatic opening of the latter 

 circuit after the first four or five oscil- 

 lations. All of the energy of the excit- 

 ing circuit is transferred to the antenna 

 during these four or five oscillations. 



The requirements for this quenching 

 effect are, first, that there be no arcing 

 at the gap ; second, that the gap be very 

 short. It appeared that the rotating gap 

 offered great possibilities as far as the 

 prevention of arcing is concerned, owing 

 to the air cooling fan effect of the mov- 

 ing studs which tends to clear the gap 



"There is also a possibility of a third oscillation. 



of ionized air or metal vapor after each 

 spark, and to the fact that each spark 

 is of relatively short duration, being in- 

 terrupted by the separation of moving 



FIG. 2. 



Powerful Free Oscillations of Single Frequency 

 Induced in the Aerial by a Highly Damped Oscilla- 

 tion Circuit. 



studs from stationary electrodes in rota- 

 tion, thus preventing temperature rise 

 and the complete formation of arcs. It 

 has not been very usual, however, to 

 truly utilize the principle of short gaps 

 with the rotary discharger, for no mat- 

 ter how closely the stationary spark 

 points are set to the plane of rotation of 

 moving points the discharge always an- 

 ticipates the exact juxta-position of pairs 

 of these points and take place over a 

 considerably longer gap than that indi- 

 cated. This is especially noticeable at 

 high voltages. 



It has been common practice to use 

 two stationary electrodes for feeding 

 energy to the revolving disk; thus, two 

 sparks occur simultaneously in series at 

 every discharge. 



The writer has recently had built a gap 

 in which, instead of only two sparks in 

 series, there are eight. By this arrange- 

 ment the total discharge voltage is dis- 

 tributed over eight gaps instead of two, 

 so that, while the total gap length through 

 the discharger remains practically unal- 

 tered, the length of the individual gaps 

 is reduced approximately fourfold. 



There is a certain peculiar advantage 

 in thus dividing the discharge among 

 several series gaps. The possibility of 

 arcing is very greatly reduced. Given n 

 gaps of equal lengths in series, the volt- 

 age required to sustain an arc in the gaps 

 is approximately n times as great as 

 would be required for a single gap n 



