15 



RESEARCH ON THE ABSOLUTE UNIT OF ELECTEICAL 



RESISTANCE * 



[American Journal of Science [3], XV, 281-291, 325-336, 430-439, 1878] 



PEELIMINAEY REMABKS 



Since the classical determination of the absolute unit of electrical 

 resistance by the Committee on Electrical Standards of the British 

 Association, two re-determinations have been made, one in Germany and 

 the other in Denmark, which each differ two per cent from the British 

 Association determination, the one on one side and the other on the 

 other side, making a total difference of four per cent between the two. 

 Such a great difference in experiments which are capable of consider- 

 able exactness, seems so strange that I decided to make a new deter- 

 mination by a method different from any yet used, and which seemed 

 capable of the greatest exactness; and to guard against all error, it was 

 decided to determine all the important factors in at least two different 

 ways, and to eliminate most of the corrections by the method of experi- 

 ment, rather than by calculation. The method of experiment depended 

 upon the induction of a current on a closed circuit, and in this respect, 

 resembled that of Kirchhoff, but it differed from his inasmuch as, in 

 my experiment, the indiiction current was produced by reversing the 

 main current, and in Kirchhoff's by removing the circuits to a distance 

 from each other. And it seems to me that this method is capable of 

 greater exactness than any other, and it certainly possessed the greatest 

 simplicity in theory and facility in experiment. 



In the carrying out of the experiment I have partly availed myself 

 of my own instruments and have partly drawn on the collection of the 

 University, which possesses many unique and accurate instruments for 

 electric and magnetic measurements. To insure uniformity and accur- 

 acy, the coils of all these instruments have been wound with my own 

 hands and the measurements reduced to a standard rule which was 



1 1 am greatly indebted to Mr. Jacques, Fellow of the University, who is an excel- 

 lent observer, for his assistance during the experiment, particularly in reading the 

 tangent galvanometer. 

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