generated in a High-tension Magneto. 155- 



The equations (37) and (41) allow the optimum value 

 o£ u ( = L 1 C ] /L 2 C 2 ) to be calculated for any given values of k 2 

 and s, and therefore the optimum capacity of the condenser 

 when Li and L 2 C 2 are known. They also allow the theoretical 

 curve to be determined showing the relation between the 

 capacity of the condenser and the maximum secondary 

 potential, or, which comes to the same thing, the curve of 

 which u is the abscissa and U sin <£ the ordinate. 



3. On the Curves showing the relation between Primary 

 Capacity and Maximum Secondary Potential. 



Examples of these curves, calculated for the case of an 

 induction-coil (5=1) have been given in a former paper*. 

 The curves consist of a series of arches which touch the 

 curve (u, U) at points corresponding with the frequency- 

 ratios 3, 7, 11, . . ., and intersect one another at the points 

 for which n 2 /n 1 = 5, 7, 9, . . . The relative proportions of the 

 arches and the number of the one in the series which stands 

 highest depend upon the coupling. Thus if P is less than 

 0'71 the first arch (containing the 3/1 point of contact) 

 stands highest ; if P is between 0'71 and 0*87 the second 

 arch contains the highest point of the curve. The vulue of u 

 at the summit of the highest arch determines the optimum 

 primary capacity for any given induction-coil, and a table 

 has been given containing the optimum values of u for 

 various values of k 2 f. 



Similar curves may be obtained experimentally b}' ob- 

 serving the spark-length of the coil for a constant current 

 and for various values of the capacity of the primary 

 condenser, or, better, by observing the least value of the 

 primary current at break which will cause a spark to 

 pass across a gap of constant width. This plan is much 

 more convenient, and it is also more accurate, because the 

 primary current at break is more nearly proportional to 

 the maximum secondary potential than is the potential 

 to the spark-length. The secondary (sparking) potential 

 being constant, the reciprocal of the least sparking current 

 is thus proportional to the maximum secondary potential 

 per unit current. 



An example of a curve obtained in this way for an 



* Phil. Mag. Aug. 1915, pp. 229, 230. 

 f L. c. p. 231. 



