

Bare Wire for Resistance-coils. 



221 



No. of Ooil. 

 1 



March 8. April 3. 

 9-9765 9-9764 



April 4. 



Mean. 

 9-9764 



2 



9-9926 9-9925 

 10-0033 





9-9925 



3 



100033 



9-9973 



100001 



100033 



4 



9-9976 



9-9974 



5 



9-9999 10-0000 



10-0000 



6 



9-9574 9-9573 





99573 



7 



9-9558 9-9555 

 9-9863 9-9858 





9-9556 



8 



9-9864 



99862 



9 



9-9748 9-9753 



9-9758 



99753 



The values of the proportional arms are : — 





lOinX 



Mar. 8. Mar. 16. Mar. 17. 

 9-9513 9-9506 99513 



April 3. 

 9-9507 



April 4. Mean. 

 9-9509 9-9509 



lOinY 



10-0106 10-0099 100103 



10-0098 



100101 100101 



Desiring to obtain a check measurement, I balanced the nine 

 '1 ohm coils against the 1 and 10 ohm standards in parallel, 

 and obtained the value '90224 at 13°, while the first five 

 coils of the dial, when balanced against the two 1 ohm coils 

 in parallel, gave '50125 at 13°'2. The actual values for the 

 sums of the nine and five respectively, as found by the 

 separate determinations, were '90259 and '50147. Of course 

 any contact-error due to the plugs would appear when the 

 values of the coils are added up. When the separate values 

 of the nine coils are added up, the contact-error will have 

 entered 18 times into the result, and for five coils 10 times ; 

 on the other hand, when the coils are measured in series, the 

 contact-error will only enter twice in each case, and the 

 differences between the two sets of values in both cases are 

 explained by the ascertained result that the contact-resistance 

 of each plug is '00002. 



It is somewhat bold to assert that an error of '00004 ohms 

 has not entered into the determination of each of the fa ohm 

 coils. The standard itself is certainly correct, as will be seen 

 by reference to its values on the various elates ; the only 

 possible explanation would be that the connecting leads of 

 the two arms had not equal resistances. A subsequent test, 

 however, proved that they were equal. I was, therefore, 

 driven to the conclusion that the contact-resistance as above 

 found was real, and not due to an experimental error. 



The resistance of the box from terminal to terminal with 

 each plug in zero was obtained in three ways. Firstly, by 

 short-circuiting the mercury-cups in one of the arms of the 

 bridge, and measuring the resistance of the leads and plugs 



