262 M. W. Weber on the Measurement of Electric 



absolute measure here discussed; for it is not possible to compare 

 every resistance directly according to this measure, while every 

 resistance can be directly compared with Jacobi's standard. But 

 considering the importance which absolute determinations of 

 measure have in many investigations, it is desirable to be able 

 to reduce all the values, made according to Jacobi's standard, to 

 an absolute measure, which can be easily effected by comparing 

 the resistance determined as above according to an absolute mea- 

 sure with the resistance of Jacobi's standard. 



Such a comparison has been made ; and it has been found that 

 the two resistances are nearly as 32 : 10, or, more accurately, as 

 19000 : 5980. But as the first resistance has been found in ab- 

 solute measure to represent 19000 million units, Jacobi's stand- 

 ard represents 5980 million units; or the resistance determined 

 according to Jacobi's measure can be reduced to absolute mea- 

 sure by multiplication by 6 milliards. By this determination 

 it would be possible to reproduce approximately Jacobi's stan- 

 dard, even if it were lost. 



§ 6. On the value of the constants found by Kirchhoff, on which 

 the intensity of induced electric currents depends. 



The induction-constant which Neumann, in his development 

 of the mathematical laws of induced electric currents, calls e, 

 has the following meaning. If W be the absolute unit of mea- 

 sure proposed as above for electric resistances, and W that mea- 

 sure of resistance which is actually used ; if, further, C be the 

 measure of velocity which forms the basis in establishing the 

 above absolute measure (1 millimetre in a second) ; if, on the 

 contrary, C be the measure of velocity actually used in mea- 

 suring the induced motions and actions of the induced currents 

 (1 Prussian inch = 26*154 millims. in a second, according to 

 Kirchhoff), we have 



__0W 



6 -^cw r 



It follows from this, that if the value of this induction-constant 

 is once determined, any resistance given according to the mea- 

 sure chosen can be referred to an absolute measure. 



In the determination of the induction-constant e given by 

 Kirchhoff in the seventy-sixth volume of Poggendorff's Annalen, 

 the resistance of a copper wire has been chosen as a standard, the 

 length of which was 1 Prussian inch = 26-154 millims., and the 

 section 1 Prussian square inch = 684 square millims. Here 

 unfortunately there is no determinate measure of resistance; for 

 different pieces of copper of the same dimensions have different 

 resistance ; and it follows, therefore, that the value of the indue- 



