ON STANDARDS FOR USK IN ELECTRICAL MEASUREMENTS. 



151 



Table X.- 



-Showing the Differences between tlie Flatinum Silver B.A. Units 

 in 1890 and in 1892. 



Table XI. — Giving Differences in Bridge Wire Divisions between the 

 Legal Ohm Standards and Flat. 



In November 1890 two new coils marked J and K were made of plati- 

 •num silver wire, supplied by Messrs. Elliott Bros. The wires of the coils 

 are wound in a loose spiral inside the case, being secured at intervals by 

 silk threads to an ebonite central stem. They are thus in contact with air 

 only, and there is no paraffin inside the case. It was hoped in this way to 

 secure freedom from the strains set up by changes of temperature in the 

 paraffin, which appeared from the results given in the ' Report ' for 1890 

 to have some connection with the changes of resistance there described. 



The results are shown in fig. 4. From the six observations for 

 each coil there recorded it is clear that there has been no change during 

 ihe time for which the observations have lasted. 



Fig. 4.— Showing the values of the B.A. Units Flat, J and K, from observations 

 between November 1890 and July 1892. 



JO » /Z f3 74 /6 K f7 /S 7S Za /O /J /2 /3 /# /5 /€ /7 fe J3 Z9 



The vertical divisions are 0005 B.A.U. 



The horizontal divisions are 1° C. 



Flat = l B.A.U. at 14°-8. Temp. Coeff. -00027 (Fleming's observations, 1876). 



•J = 1 B.A.U. at 14°-. Temp. Coeff. •000260. 



K = l B.A.U. at 14°-15. Temp. Coeff. 000261. 



