Alternate Current- Condensers. 10 7 



therefore 



Xj occos 



VKL 



and 



T = 2tt a/KL 



When a charged condenser is short-circuited through a 

 circuit with self-induction only, oscillation is produced, the 

 current and pressure both varying harmonically with a fre- 

 quency of 1/27T \/KL. 



In the Deptford case, with a capacity of two microfarads 

 and a period of 0'0125, the self-induction needed would be half 

 a henry. A choking coil with such a coefficient of self-induc- 

 tion wound to carry 250 amperes, which, I understand, is the 

 load of one main, would take 64,000 volts to get the current 

 through. A transformer only acts on the circuit as a choking 

 coil to the small extent due to the waste induction in it. If 

 built on the lines of commercial transformers, this one would 

 have to be large enough to give an output of hundreds of 

 millions of watts to produce a resonator effect. Moreover, a 

 slight alteration in the speed of the dynamo would throw it 

 "out of tune" with the resonator, so that the effect would 

 disappear. For instance, a 5 per cent, variation of speed 

 would alter the pitch of the dynamo nearly a semitone. 



It has been stated that there is a difference of apparent 

 ratio in the Deptford transformer when the main is in circuit ; 

 that is to say, that though it generally transforms 4 to 1, 

 when the main is on it tranforms about 4-| or 5 to 1. I 

 would suggest this is impossible. There is always a " drop " 

 in transformers due to waste field. In a transformer for 10,000 

 volts and 250 amperes, if properly designed, it would be well 

 under 1 per cent., probably about one tenth per cent. In 

 order that an oscillatory current should be confined to the "line" 

 side by the waste induction which causes a drop of 1 per cent. 

 and 80 periods per second, the frequency would have to be 

 enormous. Such an oscillatory current would also be ex- 

 cluded from the secondary at the London end. Any effect 

 which does not involve enormous frequencies must show on both 

 sides of the transformers. It might be said that the " drop " 

 of the transformers in the circuit would give enough self- 

 induction to produce a frequency corresponding to an upper 

 partial of the note of the dynamo. If the dynamo E.M.F. does 

 not vary harmonically, such an effect might be produced, but 

 it would show on the voltmeters at both ends. To give an 

 increase of 15 or 20 per cent, effective pressure, with a total 

 transformer drop of 1 per cent., the frequency would be, 



