Intelligence and Miscellaneous Articles. 367 



sistauce of transition. Frolich probably considers that a cannot 

 be exclusively an electromotive force, for in this case it would have 

 what, in his opinion, is the absurdly high value of 39 volts. 

 Peukert* has made a series of observations on this subject, in which 

 the strength of the current varied from 10 to 30 amperes. As 

 follows from my older observations, Peukert found that the 

 apparent resistance of the luminous arc may be represented by the 

 formula w = a -\- bl. If it be assumed that the constant a is an 

 electromotive force, its value according to Peukert must amount to 

 35 volts ; a value which appeared to him so high that he did not 

 venture to assume it could have its origin in an electromotive 

 force, but that, partly at least, it represents a resistance of 

 transition. 



Prom my investigations cited above it follows that a is inde- 

 pendent both of the magnitude of the source of the current and 

 of the strength of the current, provided this does not sink to 

 the lowest limit in which a voltaic arc may be formed. In my 

 first experiments on this subject I have calculated a as an electro- 

 motive force, expressed in Bunsen's elements. Seven successive 

 experiments made with a current of 53 to 79 Bunsen's elements 

 gave the following results : — 



a=24,416; 25,962; 25,354; 20,951; 21,637; 21,483; 23,119; 



the mean of which is =23*315. This holds when the light is pro- 

 duced between carbon points of the ordinary kind. 



If it be assumed that 1 Bunsen's element is equal to 1*7 Daniell's, 

 and that this is 1*08 volt, 1 Bunsen = l*8 volt. If this number be 

 multiplied by the mean in question, we obtain 41*97 volts. The 

 mean of this number and of that found by Prolich and Peukert 

 (39 and 35) gives 38-66 volts. 



The view favoured by some experimenters, that the constant a 

 partly represents a resistance of transition, is in fact disproved by 

 the investigations of Victor von Langf. By an ingenious method 

 Lang succeeded in proving that the voltaic arc does contain a counter 

 electromotive force which is equal to 39 volts. As this value of the 

 counter force in the arc is almost equal to the value of the constant 

 a above given, it follows that there is no resistance of transition in the 

 voltaic arc, and that therefore the entire diminution of the strength of 

 the current which results from the production of the arc-light is caused 

 by the resistance of the arc bl, and by the electromotive force contained 

 in it. 



It must, however, be remarked here, that since the determinations 

 of the values of a and of the electromotive counter force contained 

 in it may possibly have been made with carbon electrodes of 

 different kinds, it would be desirable to repeat both determina- 



* Electrotechn. Zeitschrift, vol. vi. j>. Ill (1885). 

 t V. von Lang, Wien. Ber. April 1885 ; Wiedemann's Annalen. 

 vol. xxvi. p. 145 (1885). 



