190 Prof. H. F. Weber on Electromagnetic and 



absolute determination of the electromotive force active in the 

 circuit, we obtain the equation 



jq(i + ^)=«e, 



III. If we then determine, according to one of the galvanic 

 methods usually employed, the value of the same electromo- 

 tive force in relative measure (let e denote this value) — say, 

 on the basis of the absolute electromagnetic unit of current 

 and the Siemens unit of resistance, — then by combining the 

 two measurements a new mean will be obtained to determine 

 the absolute electromagnetic value of the relative unit of re- 

 sistance made use of : the absolute value of the latter is 



1 S. M. U. = -• 



e 



provided that the current-intensity i in the equation 



which served for determining E, was likewise measured accord- 

 ing to electromagnetic measure. 



I have carried out a series of absolute and relative measure- 

 ments of the electromotive forces of the elements of Daniell 

 and Bunsen according to procedures II. and III., in order to 

 be able to derive the absolute value of the S. M. U. by a third 

 method totally different from the two already described. When 

 selecting this process I had a secondary object also in view — 

 to submit to as rigorous a trial as possible the correctness of a 

 singular result obtained by M. Favre, which directly contra- 

 dicts a great number of galvanic experiences. In this opera- 

 tion one of my pupils, M. Kudio, rendered me important as- 

 sistance. 



In the circuit of the Daniell or Bunsen pile employed, con- 

 sisting of 7-10 elements, the platinum wire wound upon a 

 hardgum frame, previously used, was placed in the already- 

 mentioned water calorimeter. The resistance w of the pla- 

 tinum wire was known accurately for all the temperatures 

 employed. The resistance w l of the rest of the circuit, in 

 which, as an essential part of the resistance, the pile was com- 

 prised, was determined simultaneously with the electromotive 

 force of the latter, by a process resembling that described by 

 Mr. Mance*. A path for the current was constructed after 

 the fashion of Wheatstone's bridge-process ; the place of the 



* Proceedings of the Koyal Society, vol. xix. 1871, p. 248. 



