of the Coefficients of Induction. 467 



the two cases, the swing which measures it will be greater in 

 that case for which the time-constant is the smaller. 



13. Evidence of hysteresis was obtained in a very marked 

 way from a 2 H.P. transformer lent to Professor Ayrton by 

 Mr. Kapp. The coefficient of self-induction of the primary 

 coil was measured when different currents were traversing 

 the secondary. The magnetizing current (denoted by A) 

 was obtained from accumulators, and varied up to 10 amperes. 

 It was sent in both directions, and its value was read by an 

 Ayrton and Perry ammeter. The coefficient was obtained 

 either by comparison with a standard condenser by the 

 swing-method already described or by the secohmmeter. 

 The test-current used to obtain the coefficient was - 037 

 ampere for the swing method and '01 ampere for the sec- 

 ohmmeter method. In the former case means were provided 

 for sending the test-current round the primary in either 

 direction at will, so that the swings obtained corresponded 

 either with the slope PA (see fig. 1) or with the slope PB. If 

 the total current through the transformer-coils were alternated 

 between two values corresponding with the points A and C, 

 the slope AC was found not only to be less than the preceding 

 slope PA but greater than the succeeding slopes CD, and in 

 some cases several successively diminishing values were 

 obtained. The coefficients corresponding with the slopes 

 PA, AC, and CD will be respectively denoted by the letters 

 Lp, L r , and L e . The values obtained could only be reproduced 

 when the magnetic history of the iron was exactly repeated ; 

 and whatever the process of magnetization was, the numbers 

 obtained at corresponding parts of successive cycles gradually 

 diminished until the true cyclic values were obtained. 



Thus the values obtained by the swing-method for the pro- 

 gressive coefficient h p were "087 secohm or "192 secohm, 

 according as the value of A had been diminished to zero from 

 1 ampere or from 6 amperes. When A was 1 ampere, values 

 of h p could be obtained varying between '074 and "130 secohm, 

 according to the previous history, and simultaneously the 

 values of the return coefficient L,. could be varied between 

 •032 and *053 secohm. The values of the cyclic coefficient 

 L c (which were obtained by reversing the test-current several 

 times before taking the swing) were, however, fairly constant, 

 and were *029 secohm when A was zero and "016 secohm 

 when A was 6 amperes. 



In order to obtain a complete set of values for the coefficients 

 L p and Lc, it was necessary that the iron should go through 

 the same magnetizing processes before any reading was taken. 

 The magnetizing current was therefore diminished to — 10 



