ON STANBABDS FOR USE IN ELECTEICAL MEASUKEMENTS. 

 B.A. Units. 



207 



Of these the coils Elliott Nos. 41, 56, and 117 have been tested 

 before, but owing to the green coloration mentioned in the last report 

 showing itself in the paraflBn, the paraffin was removed and the coils 

 refilled with ozokerit, which can be obtained more nearly free from traces 

 of acid. 



This change in all cases produced an appreciable increase in resistance, 

 amounting in the case of Elliott No. 41 to about -0025. 



The coils ^ 63, 68, and 69 are three of the original B.A. units. 



70 is a coil sent over from the Johns Hopkins University for the 

 purpose of connecting their value of the B.A. unit with that found at the 

 Cavendish Laboratory. 



Shortly after the Birmingham meeting of the Association the Secretary 

 received a letter from the Board of Trade enclosing a copy of the general 

 bases of a convention proposed by the French Government for the con- 

 sideration of the Powers, with the object of carrying out the resolutions of 

 the Paris Congress with regard to electrical standards. 



The convention stipulates that a legal character is to be given to 

 (1) the legal ohm ; (2) the ampere ; (3) the volt ; (4) the coulomb ; 

 (5) the farad. 



It charges the Bureau International des Poids et Mesures, established 

 by the Metric Commission, with the construction and conservation of the 

 international prototypes of the standard of electrical resistance, the com- 

 parison and verification of national standards and secondary standards. 



These questions had, at the request of some of the English delegates 

 to the Congress of 1883, been considered by the Committee at the 

 Birmingham meeting, and the following series of resolutions, which the 

 Secretary was instructed to forward to the British Government, had been 

 agreed to on the motion of Sir William Thomson, seconded by Professor 

 W. G. Adams :— 



(1) To adopt for a term of ten years the legal ohm of the Paris Con- 

 gress as a legalised standard sufficiently near to the absolute ohm for 

 commercial purposes. 



(2) That at the end of the ten years period the legal ohm should be 

 defined to a closer approximation to the absolute ohm. 



