420 



Mr. J. H. Reeves on an Addition 

 Table IV. 



After the current had flowed continuously for 3 minutes 

 6 amperes as before. 



X. 



Observation. 



R. 



119 

 118 

 117 



28 divs. deflexion left. 



4 „ „ left. 



20 „ „ right. 



0-0011784 



The difference between these two results is about £ per 

 cent., while the deflexions are more than sufficient for an 

 accuracy in It of 0*1 per cent. 



A few days later these experiments were repeated with a 

 current of 2 amperes. The slight discrepancy in the value of 

 R was due to the fact that in the interval the cable, which 

 was not quite straight, had been removed. On replacing it a 

 slightly less length must have been included between the 

 knife-edges. As, however, these experiments were being 

 made solely to find the sensibility of the measuring arrange- 

 ment, no attempt was made to straighten it. The results are 

 shown in Table V., experiment (a) being for the short dura- 

 tion of current, and (b) the result after the current had flowed 

 continuously for 3 minutes. 



Table V. 

 Current 2 amperes. 



Experiment. 



X. 



Observation. 



R. 





f 



119 



16 divs. deflexion left. 



] 





(a) 



{ 



118 

 117 



3 „ „ left 

 10 „ „ right. 



1 



0-001178 



(ft) 



{ 



118 

 117 



4 „ „ left. 

 9 „ „ right. 



i 



0001177 



From the above results it will be seen, firstly, that 13 

 divisions correspond with 1 ohm difference in x, thus making 

 the fourth significant correct, in other words, an error in R is 

 less than 0*1 per cent. ; and secondly, the passage of a current 

 of 2 amperes only produced in 3 minutes a difference of like 

 amount. 



No larger cable was tried, nor was any wire smaller than 



