ON THE INDUGTION-COIL. 



BY 



LORD RAYLEIÇtH. 



Although several valuable papers relating to this subject have re- 

 cently been published by Oberbeck *), Walïer 2 ), Mtzuno 3 ), Beattie 4 ) 

 ancl Klingeleuss 5 ), it can hardly be said that the action of tlie instru- 

 ment is well understood. Perhaps the best proof of this assertion is to 

 be found in the fact that, so far as I am aware, there is no a pilori cal- 

 culation, determining from the data of construction and the value of 

 the primary current, even the order of magnitude of the length of the 

 secondary spark. I need hardly explain that I am speaking here (and 

 throughout this paper) of. an induction-coil working by a break of the 

 primary circuit, not of a transformer in which the primary circuit, 

 remaining unbroken, is supplied with a continuously varying alterna- 

 tin g cnrrent. 



The complications presented by an actual coil dépend, or may dépend, 

 upon several causes. Among thèse we may enumerate the departure of 

 the iron from theoretical behaviour, whetlier due to circumferential 

 eddy-currents or to a failure of proportionality between magnetism and 

 magnetizing force. A second, and a very important, complication lias 

 its origin in the manner of break, which usually occupies too long a 

 time, or at least départs too much from the idéal of an instantaneous 



*) Wied. Ami. 62, p. 109, 1897; 64, p. 193, 1898. 



') Wied. Ann. 62, p. 300, 1897; 64, p. 623, 1898. 



:! ) Phil. Mag. 45, p. 447, 1898. 



*) Phil. Mag. 50, p. 139, 1900. 



5 ) Ann. der Physik 5, p. 837, 1901. 



