PRACTICAL STANDARDS FOR ELECTRICAL MEASUREMENTS. 



39 



The observations recorded are in terms of B.A. Flat. Owing to a 

 change in Flat taking place, however, the 1903 comparisons were made 

 chiefly with Nalder 3715. 



In Table I. the approximate difference in B.A.U. between Flat and 

 the B.A, unit coils F, G, H of the Association are given. 



Table II. gives the difference in ohms between^ ( 1-01 3-58 x Flat) and 

 other platinum-silver coils. Temperature of observations, 16° C. 



Table I. 



Table II. 



Table III. shows the percentage difference between (10] 358 x Flat) 

 and the unit of two 10-ohm platinum-silver coils of the Association 

 at ] 6° C. 



Table III. 



The coils F, G, and H are similarly constituted : they are the old 

 B.A. coils made by Matthiessen. No. 3715 is by Nalder Bros., and the 

 remainder of the coils by Messrs. Elliott Bros. No. 264 is a coil belonging 

 to the Board of Trade, and has been returned to "Whitehall ; hence there 

 are no observations for 1903. 



Tables I., II., and III. assume Flat to be constant. It will be observed 

 that the differences of Flat and 3715, 270, 288, and 289 are constant from 

 1897 to 1901. From 1901 to 1903 a change of about -017 per cent, 

 is evident between Flat and the coils 3715, 264, 269, 270, and again 

 between Flat and the units of the coils 288 and 289. This suggests a 

 change in the value of Flat from 1901. 



Since 1901 comparisons between Flat and the manganin standards of 

 the Association have been made. Table IV. gives the observed values in 

 ohms. 



' 1 B.O.T. ohm = 101358 B.A.U. 



