68 Mr. E. H. Griffiths on the Influence of 



Table II. 



Potential-difference 

 (in terms of a Clark cell). SB, (in true ohms). 



1 -00087 



2 . . -00227 



3 ...... . -00433 



4 -00723 



The resistance of the coil was carefully determined for 

 each group of experiments, at the mean temperature of the 

 group, and also occasionally at a fixed temperature, in order 

 to trace any change. During the first series a slight increase 

 was observable (apart from the natural increase due to its 

 temperature-coefficient). This was possibly a consequence 

 of an oversight on my part, as I had forgotten to previously 

 anneal the wire. After it had been raised to the highest 

 temperature attained during these experiments the further 

 change became negligible. 



The absolute value of Rj was obtained by means of the 



dial-box described in paper J, pp. 408-10. The errors of the 



separate coils and of the coils in the bridge-arms had been 



ascertained by a direct comparison, which had been made by 



kind permission of Mr. Glazebrook, with the B.A. standards 



in the autumn of 1892. 



dO 

 Y II. The value of — x at several points of the range (which 



was usually about 15 centim. of the bridge-wire, i. e. about 

 1°*4 C.) having been ascertained, the results were plotted 

 (with 1 as abscissa) in order to ascertain the regularity &c. 

 of the observations, which was generally found to be satis- 

 factory. The values of-^ at the readings 60 and 70 of the 



bridge-wire were then obtained and divided by n 2 . Three 

 experiments having been performed at each temperature with 

 three different values of n, the intersection of the three lines 

 thus found gave 0^, the ordinate for that abscissa giving the 

 rate of rise due to the electrical supply alone. A plan of 

 these intersections is given on Plate I. 



A glance at Plate I. will show that the null point in each 

 jcase is not accurately defined. 



The intersection of the 3- and 4-cell lines is always to the 

 left of the other intersections. 



