64 



KEPOBX 1888. 



The other coils, with perhaps the exception of F, would lie at 0° on the 

 straight line which represents the observations between 10° and 20" 

 ■within the limits of the errors of experiments. 



The numbers given in Table VIII. agree well with those found by 

 Fleming in 1880 with the exception of the coils A and B. 



Some observations made at intermediate temperatures are in agree- 

 ment with the statements just made. • Thus on March 2, the tempera- 

 ture of the room being 12°, we found that at 4°9 C. the difference between 

 A and Flat at was 256 bridge wire divisions, while for B at 4°'8 the 

 difference was 280 bridge wire divisions. 



Thus in conclusion we infer that while the observations in 1880 and 

 1888 are in close accord for temperatures between 10° and 20° there is a 

 discrepancy between them at lower temperatures for the two coils of 

 platinum iridium A and B. The other coils, however, do not show any 

 marked evidence of change. For the same two coils there is a discre- 

 pancy between our results and those of Chrystal in 18/G and Hockin in 

 1867. For the other coils the agreement between Chrystal and ourselves 

 is as close as can well be expected, and our results as well as those of 

 Chrystal agree with Hockin's for the gold silver coil C and the platinum 

 coils J) and E. According to both Chrystal and ourselves the platinum 

 silver coils have fallen in value relatively to the others by something like 

 •0006 B.A.U., corresponding to change in the temperature at which they 

 are correct of some 2° Centigrade. We have seen, however, that G, the 

 only one of these coils which was carefully examined by Chrystal in 1876, 

 has not altered since. In its case the whole fall, if it occurred at all, took 

 place between 1867 and 1876, and we suggest that possibly the fall has 

 not been a real one, but merely apparent, owing to the use of the wrong 

 temperature coefficient by Hockin. 



As has been said already, the value that has been assumed as the 

 Mean B.A. Unit since Fleming consti-ncted his chart in 1876 is the mean 

 of the values of the six coils A, B, C, D, E, and G mentioned in the 

 Report for 1867 at the temperatures at which they were then said to be 



' This coil is not mentioned in the Report of 1867. 

 the label. 



The details given are from 



