508 31. I. jPupirir— Electrical Oscillations of 



ble to add capacity to the terminals of the secondary coil then 

 the speed of the alternator must be below this critical point. 



b. By diminishing the speed it is possible to increase the 

 terminal capacity without diminishing perceptibly the second- 

 ary voltage. Hence the secondary current will be thereby 

 increased and therefore the physiological effect of a lower fre- 

 quency Tesla current may be considerably more powerful than 

 that of the higher frequency. 



c. At very high frequencies, say 10 4 periods per second the 

 Tesla current will in general be exceedingly small, considering 

 that the impressed e. m. f. of his generator is about 140 volts 

 only. Hence the physiological effect of these currents will 

 also be small. (But I do not wish to be understood as deny- 

 ing that the rapidity of reversals in itself diminishes the 

 physiological effect.) 



d. Since the rise of potential will be the higher the smaller 

 the dissipation of the work which the impressed e. m. f. does 

 it is evident that dielectric hysteresis, in consequence of which 

 the dielectrics are heated, will pull down considerably the sec- 

 ondary voltage. It is therefore desirable to employ liquid or 

 solid dielectrics of small specific inductive capacity, since in 

 these the heating due to dielectric hysteresis is smaller than in 

 dielectrics of high inductive capacity. 



e. It is evident that by a suitable diminution of the coefficient 

 of mutual induction M within the limits within which p 2 M 2 is 

 considerably larger than RS for the highest value of S at 

 which the high frequency system is expected to run both the 

 secondary current and the secondary e. m. f. can be increased 

 very considerably. This* could be done by dividing the sec- 

 ondary coil into two parts and allowing one part only (and 

 that too probably the smaller part) to surround the primary 

 coil, in which case the remaining part would be employed as 

 additional inertia coil in the secondary circuit, this inertia coil 

 performing the function of assisting the impressed e. m. f. to 

 produce a high rise of potential in the secondary circuit. In 

 one of his papers* Mr. Tesla mentions that, by removing partly 

 the primary coil from the secondary, higher potentials can 

 sometimes be produced, and the output of the secondary cir- 

 cuit very much increased. " St. Elmo's Hot Fire " is the 

 name which Mr. Tesla gives to the powerful flame discharge 

 obtained, by this arrangement of the two coils, from one of the 

 secondary poles, when the other pole (the terminal of the 

 secondary turns which are nearest to the primary coil) is con- 

 nected either to the primary or to a body having considerable 

 capacity. Mr. Tesla states that his object in arranging the 



* See Mr. Tesla's article cited above, p. 23. 



