[ 172 ] 

 XII. Intelligence and Miscellaneous Articles. 



ON THE FUNCTION" OF THE CONDENSER IN A RUHMKORFF's COIL. 

 BY B. WALTER. 



1\/f R. T. MIZUNO has recently described in this Journal* some 

 -L*-*- experiments on the influence of the dimensions of the 

 primary condenser of a BuhmkorfPs coil on the length of the 

 secondary spark ; the result of these experiments may be briefly 

 stated to be that the most favourable dimensions of the condenser, 

 that is those which give the longest spark with a given apparatus, 

 are not constant, but greater the stronger is the primary current 

 used. In connexion with these investigations Mr. Mizuno has 

 raised doubts against the validity of the formula, which I arrived 

 at theoretically t, 



E 



-Wk 



in which E 2 is the maximum value of the tension of the secondary, 

 l x is the strength of tlie primary current immediately before 

 breaking, L 2 is the coefficient of self-induction of the primary 

 condenser. 



I venture to reply, in the first place, that the fact observed by 

 Mr. Mizuno is due to the brealc-sfarlc increasing with increase of the 

 current, so that a larger condenser is necessary in order to suitably 

 enfeeble the spark. I have explicitly deduced the formula given 

 above on the assumption that the break-spark could be neglected ; 

 and it is a matter of course that a phenomenon the existence of 

 which is entirely due to the occurrence of this spark cannot be 

 expressed by that formula. 



I may perhaps be permitted to take this opportunity of insisting 

 that the above formula does not claim to express an exact mathe- 

 matical relation between the quantities in question, but is rather 

 only a first approximation to the truth, which with the very com- 

 plicated processes in the induction-coil will always possess a certain 

 A r alue, the more so that the important quantities I v L 2 . and C x are 

 contained in it in a simple form, and at any rate with some 

 approximation. 



A second, but much more complicated approximation is found 

 in Colley's excellent paper J, which is mentioned by Mr. Mizuno, 

 and Oberbeck§ also has shown that my formula may, making 

 certain limitations, be deduced from the more general one of 

 Mr. Oolley. — Communicated by the Author. 



Hamburg phvsikalische Staatslaboratorium, 

 May, 1898. 



* Phil. Mag. xlv. p. 447 (1898). 



t B. Walter, Wiedemann's Annalen, lxii. p. 300 (1897). A complete 

 and intelligent abstract of this research is given in the ' Electrical Review,' 

 vol. xli. pp. 529 and 597 (1897). 



X R. Colley, W T ied. Ann. xliv. p. 109 (1891). 



§ A. Oherbeck, Wied. Ann. lxiv. p. 193 (1898). 



