ROSA AND WOLFF: INTERNATIONAL ELECTRICAL UNITS 261 

 1. RESISTANCE COMPARISONS 



Each delegate brought with him one or more resistance stand- 

 ards with the object of furnishing data on the relative values of 

 the unit of resistance employed in the four laboratories, and of 

 deriving a basis for the voltameter measurements made in Wash- 

 ington. The results obtained also served the further purpose 

 of establishing the magnitude of one of the corrections to be 

 applied to the voltameter measurements previously made by 

 the delegates, to reduce them to a strictly comparative basis. 



The necessary electrical comparisons were all made in a ther- 

 mostatically controlled and well stirred oil bath, the standards 

 being substituted in turn in the same arm of a Kelvin double 

 bridge. The connecting resistance between the standard and an 

 auxiliary 1-ohm coil was so small as to require no adjustments of 

 the auxiliary (10-ohm) bridge arms, the coils under comparison all 

 having approximately the same values, and the resistance of 

 the connections to the auxiliary bridge arms being very low. 



The results of the comparisons of the different metallic resist- 

 ances were as follows: 



Ohm PTR - Ohm NBS = + 2 X 10-* 

 Ohm NPL - Ohm NBS = + 12 X 10~ 6 



From these can be deduced that the differences between the 

 values of the ohms in use in the different laboratories, and as 

 represented by the coils brought to Washington, and the value 

 adopted by the technical committee are as follows : 



For the PTR ohm - 5 X lCh 6 

 For the NPL ohm + 5 

 For the NBS ohm - 7 

 For the LCE ohm + 110 



The relative measurements of the metallic resistances showed 

 that the resistances inclosed in sealed boxes gave, during the 

 experiments in Washington, results more regular than the metal- 

 lic resistances for which this precaution had not been taken. 



The Technical Committee therefore decided to choose, actually 

 and until new mercury ohms shall have been constructed, as the 

 value of the international ohm, to be recommended to all coun- 



