232 Prof. E. Taylor Jones on most Effective Primary 



For any one of these values of k 2 the greatest maximum 

 secondary potential is found (on the assumption of negligible 

 resistances and perfect interruptions) by multiplying the 

 corresponding value of U sin cp (fifth column) by the factor 

 L 2 i?o/ VL2C2. If this factor is constant in all these adjust- 

 ments the numbers in the fifth column are proportional to 

 the greatest maximum secondary potential. This case is 

 considered in the next section. 



The greatest maxima of U sin <£ are also shown in fig. 3 

 plotted as a carve, from which may be found the value 

 corresponding to any degree of coupling within the same 

 range. 



It will be seen from the Table that for the higher values 

 of P the greatest maxima of U sin <£ correspond very closely 

 to coincidences (<£ = 7r/2), and that this applies with con- 

 siderable accuracy down to the value 0'71 of P. Even at 

 this degree of coupling the 7/1 coincidence value of U sin <£ 

 (approximately 1*134 at w = 0*07b') only differs by 4 parts in 

 1100 from the neighbouring maximum value (1-138) given 

 in the Table. The rule, already stated in a former paper*, 

 that the optimum primary capacity is that which determines 

 the coincidence nearest to the maximum value of U, applies 

 therefore with sufficient accuracy for all values of k 2 between 

 0-92 and 0*71. 



The more exact value of the optimum capacity, or rather 

 of the optimum ratio L 1 C 1 /L 2 C 2 , for any value of k 2 within 

 these limits may be found by plotting the (P, it) curve from 

 the values given in the Table. This curve has two distinct 

 segments, one covering the range P = 0'92 to - 87, the other 

 running from 0'87 to 71. At those values of k 2 for which 

 there are two equal greatest maxima of U sin (f>, it is better 

 in practice to choose the greater of the two values of 11, since 

 the larger capacity involved does not so readily allow trouble- 

 some sparking at the interruptor. 



Over the lower range of values of k 2 , -viz. 0*71 to 0'5, 

 the greatest maxima of U sin <f> do not correspond so closely 

 with the 3/1 coincidences, except near the value P = 0'571. 

 For this range, however, a simpler and more accurate rule 

 may be stated. It will be noticed from Table I. that there 

 is, within these limits, no great variation in the optimum 

 value of u. It should also be noted that, for such values of 

 k 2 , Usin</> varies very slowly with u near the greatest maxi- 

 mum : these portions of the (u, U sin 0) curves are very 

 flat-topped. We shall therefore make only a verv slight 

 error if we take u as constant and equal to the mean value 

 * Phil. Mag. xxvii. p. 584 (1914). 



