L=44'4 x 1553 centim., R=-97 x -0492 x 10 9 - Ce 



sec. 



486 Lord Rayleigh on the Self-induction and 



sistance to steady currents was *92 inch. The resistance to 

 the periodic currents was *97 with secondary open, and 1*74 

 with secondary closed. 

 Taking then 



lr=4< 



we get 



ff 2 M 2 10" x 1-951 _, qqg 



R 2 +i? 2 L 2 ~~ 10 17 x -023 + 10 17 x 2-071 " 



According to the formula, therefore, 



1/ = -068 L = -068 x 44-4 = 3°-0, 



which is to be compared with the observed 3°*4. 



The application of the formula to the calculation of E/ is 

 somewhat embarrassed by the observed difference of resist- 

 ances to steady and to periodic currents when the secondary 

 was open, of which the theory takes no account. It is true 

 that the difference is small, but it appeared to lie outside the 

 limits of error of observation. It is not accounted for merely 

 by the tendency of periodic currents to adhere to the outer 

 parts of a conducting cylinder. If this observation stood 

 alone, one would be inclined to attribute the discrepancy to 

 some action, whether electro-magnetic or electro-static, of the 

 neighbouring secondary, even though open ; but, as we shall 

 have occasion to notice, a similar tendency of the resistance 

 to increase when periodic currents are substituted for steady 

 ones is to be observed in cases where no such explanation is 

 available. The effect was, however, too small to be investi- 

 gated further without some modification in the apparatus, or 

 in the nature of the conductors submitted to examination. 



If we take, as found for the periodic currents, R = *97, we 

 get 



R' = l-93 X -97 = 1-87, 



instead of T74 as observed. On the other hand, if we take 

 R=*92, we get 



R' = l-93x -92 = 1-77. 



The next experiment was contrived to illustrate the beha- 

 viour under periodic currents of a system composed of two 

 conductors connected in parallel. The general theoretical 

 formulae are given in a former paper*; but the more special 

 case selected for experiment was one in which the mutual 

 induction of the two conductors (M) and the self-induction of 

 * Phil. Mag. May 1886, formula* (13), (14), p 377. 



