On a new Form of Resistance-Balance. 109 



of a wire should behave differently ; for the slightly heavier 

 loading of its upper parts could hardly, according to the above 

 investigation, explain this anomaly, at least after the state of 

 the wire has become constant. 



The present experiments show that the experimental por- 

 tion of this field of research still needed extension ere it would 

 be possible to arrive at an exhaustive theory of the phenomena 

 of imperfect elasticity, in which, after determining the static 

 (i. e. the mean) positions of equilibrium of the molecules 

 executing their thermal vibrations, one might also enter upon 

 the direction of the latter. 



I hope shortly to be able to make further communications 

 upon the subject here treated, and especially on its relations to 

 magnetism. 



Leipzig, January 1879. 



XIII. On a new Form of Resistance-Balance adapted for 

 comparing Standard Coils. By J. A. Fleming, B.Sc. 

 (Univ. Lond.), Scholar of St. Johns College, Cambridge*. 

 [Plate IV.] 



1. rpHE British- Association Committee on electrical stan- 

 J- dards concluded their valuable labours on the unit of 

 resistance by constructing copies of the selected standard. 

 Certain of these coils, some fourteen in number, are at pre- 

 sent preserved in the Cavendish Laboratory, Cambridge. It 

 is important that these coils, which consist of wires of various 

 alloys, should be from time to time carefully compared toge- 

 ther in order to determine whether the ratio of their resist- 

 ances at definite temperatures remains the same f. Observa- 

 tions ought also at the same time to be made of the tempera- 

 tures at which they agree, and also of their coefficients of 

 variation of resistance with the temperature. In using for 

 the purpose the ordinary form of divided-metre bridge, seve- 

 ral objections present themselves which render it a tedious 

 process to determine accurately the difference in the resist- 

 ance of two coils at different temperatures, and hence to deduce 

 their variation-coefficients. It seemed, on consideration, that 



* Communicated by the Physical Society, having been read December 

 13th, 1879. 



t A detailed and most careful comparison of these coils was made by 

 Prof. G. Chrystal and Mr. S. A. Saunder in 1875 ; and their Eeport 

 is printed in extenso in the Report of the British Association at Glasgow 

 in 1876. This is the most recent occasion on which these coils have been 

 examined. 



