746 INDUSTRIAL APPLICATIONS. 



it is advantageous, as Cazin* has done, to use batteries or Leyden 

 jars, arranged in cascade (95). 



1289. It is somewhat difficult to take account of all the effects 

 of an induction coil, since the spark, on breaking, introduces into 

 the principal circuit a rapidly varying resistance, which plays the 

 most important part in the character of the induced discharge. 

 We may form an idea of the play of the apparatus by supposing 

 that the two circuits are closed, and that the coil is used as dis- 

 tributor, with a sinusoidal electromotive force of very short period 

 in the primary circuit. We have then sensibly A'L' = AM. 



The maximum electromotive force on the induced wire is 



L' R 



If U and U' are the volumes of the wires, y and y' their 

 diameters, if the thickness of the insulating layer is proportional 

 to the diameter of the wire in the two coils, the ratio of the re- 

 sistances R' and R is (726) 



But we have (1287) 



R; = u;/7V 



R U \//' 



U \3" 



consequently 



K/4W 

 R \3j N* 



Lastly, the ratio of the coefficients M and L' is sensibly equal 

 to the ratio of N to N', which gives 



A'R'_ /4\ 2 N' 

 AK. \3/N ' 



The maximum electromotive force developed on the induced 

 wire is then proportional to the number of turns. 



* CAZIN. Comptes rcndus, Vol. XLVI., p. 307. 1863. 



