192 Prof. H. F. Weber on Electromagnetic and 



time z and bring it into the calculation. Such variations were 

 regularly ascertained ; but they did not exceed very narrow 

 limits. As these small variations of w 1 and e have their phy- 

 sical cause in processes which run proportionally with the time, 

 it is permitted to put, instead of their mean values during the 

 time z, the mean values given by the initial and final observa- 

 tions. If the initial values of the relative electromotive force 

 and the resistance w 1 be called respectively e 1 and w?/, and the 

 final values e" and iv/', understanding by E the mean value 

 of the absolutely, and by e that of the relatively measured 

 electromotive force, and let iv a represent the value of the pla- 

 tinum resistance corresponding to the temperature t a of the 

 environment of the calorimeter, we have for the determination 

 of the quantities E and e the two equations : — 



and 



e' + e" 



From this we can derive the absolute value of Siemens's 

 resistance-unit : 



1 S. M. U. = -• 



e 



I give in the following the results of the experiments which I 

 have carried out with the cooperation of M. Rudio. In the 

 calculation of the experiments J was supposed equal to 428*55 

 m.-k., equal to the mean of the values resulting from our 

 experiments on galvanic heat-evolution and from the experi- 

 ments on the thermal behaviour of the permanent gases. 



Experiment 1. Bunsen's element — freshly amalgamated zinc, 

 sulphuric acid of sp. gr. 1'035, commercial nitric acid of sp. 

 gr. 1*365, gas-coal. 



< = 7-683 S. M. U., < x = 7-449 S. M. U., ^ = 19-873, 



,- = 19-734, E = 18-885xlO"( millim - l ^ il l ^Y 



\ sec. / 



Mean values. 



w 1= = 7-566 6=19-804. 



Result. 



1S . M . U . = E =0 . 9536xl010 /millimA 

 e \ sec. / 



