Capacity for Induction-coils and Tesla Coili 



233 



-over this range. The values of U sin <j> obtained in this way 

 do not in fact differ by more than 1 in the third place of 

 decimals from the maximum values given in the Table. 

 Hence the rule may be stated : — If k 2 lies between 0*71 and 

 0'5 the optimum primary capacity is that which makes 

 LA = 0-4:3 L 2 C 3 . 



Of the adjustments specified in Table I. three give unit 

 efficiency when the resistances are neglected, and the efficiency 

 is least at & 2 = 071, one of the casesof equal greatest maxima. 

 In this case rather over 8 per cent, of the initial energy 

 •JLi/o 2 appears as electrostatic energy in the primary con- 

 denser and electrokinetic energy in the primary circuit at 

 the moment when the secondary potential reaches its greatest 

 value. It can be shown that of this 8 per cent, about one 

 quarter represents the energy of charge of the condenser, 

 the remainder the energy of the primary current. How 

 this percentage is affected in practice by the resistances may 

 be considered on a future occasion. 



On the use of Series Inductance in the Primary Circuit. 



The series of adjustments given in Table I., or a portion 

 of the series, may be effected with an induction-coil in various 

 ways, among which the method of reducing P by the addition 

 of series self-inductance to the primary circuit is the most 

 important if we keep in view the object of obtaining the 

 greatest spark-length with a given current. In this process 

 the quantities L 21 and L 2 C 2 J»re constant, so that the values 

 of U sin cf> in the fifth column of the Table are proportional 

 to the maximum secondary potential attainable at the inter- 

 ruption of a given primary current. The optimum value of 

 the ratio L 1 Ci/L 2 C 2 for any value of k 2 is given in the second 

 column. 



In fig. 3 the greatest maxima of II sin <£ are plotted as a 

 ■curve the abscissa of which represents 1/A 2 , this quantity 

 being proportional to the total self-inductance of the primary 

 circuit. The full-line curve, the ordinate of which is pro- 

 portional to the greatest maximum secondary potential at 

 each stage, consists of three portions A, B, C, corresponding 

 to adjustments in which the frequency-ratio n 2 /n 1 is near 

 3, 7, 11 respectively. The points at which these sections of 

 the curve meet represent those cases in which there are two 

 equal greatest maxima of V 2 . The broken-line continuations 

 of the curves at these points correspond to secondary maxima 

 in the (w, U sin <p) curves. At each of these points of inter- 

 section also the efficiency is a minimum for "optimum" 

 adjustments. 



