232 M. W. Weber on the Measurement of Electric 



The greatest deflection a of the needle set in oscillation is known 

 by direct observation; and the following- expression is obtained 

 for it from the above velocity, from known laws of oscillation, by 

 multiplying by the length of oscillation / and dividing by the 

 number tt : 



rr im 



For the length of oscillation we have the known equation 



7T7tK 



mT= -tF ; 



from which 



mt _ 7T7T 



and thus 



_ irtrrr is 



Now a is obtained by direct observation ; and hence for deter- 

 mining i we have 



irirrr s 



Remembering that the current passing through the circle B also 

 traverses the circle A, we might also calculate the action of the 

 circular current A upon the needle in C ; but, for the sake of 

 simplicity, it may be assumed that the distance AC is so great 

 that this action vanishes in comparison with the action of the 

 circular current B ; in that case the actually observed deflection 

 of the needle in C gives directly the value of a. 



Consequently, by the electromotive force eE, expressed in an 

 absolute measure, for which has been found the expression 



s 

 a current is produced, in the whole closed conductor whose space 

 is to be measured, the intensity of which is expressed in an abso- 

 lute measure by il, in which 



R» t 

 i = • - • la 



irirrr s 



has been found. But, according to the unit explained in the 

 preceding paragraph, the desired resistance of the whole closed 

 conductor is expressed by ivW, in which w is determined by the 

 relation of the numbers e and i ; for 



e ttV 



w =l = m« 



Hence the execution of the measurement of an electric resistance 



