66 



EEPOBT — 1888. 



that this fall is just abont the same as that observed in tlie platinum 

 silver units of this Committee- — F, G, and H. We shall refer to it again 

 in connection witb the next series of observations. 



But by far the most important series of coils are a set belonging to 

 Mr. H. A. Taylor. Witli regard to tbem he writes : — ' Most of my coils 

 belonged to Hockin long before I knew him, and at his death they were 

 given to me by his father.' ' The early history of these coils is lost, unless 

 it can be found in Matthiessen's note-books. I am informed, however, 



that the one unit coil I sent you both last year and this, !^ No. 68, was 



copied by Hockin from the B.A. coils you now have at Cambi-idge at the 

 time when he had regular access to them. Whether from a particular 

 standard or from the mean of several, I do not know ; bat he considered 

 it to be at 15°-5 C. less than B.A. Unit by -0003. I presume the Au Ag 

 coils, Nos. 19 and 34, were verified by Matthiessen and Hockin, as they 

 have the formal B.A. stamp. With regard to the tens, one, I think, 

 belonged to Hockin and the other was purchased by Messrs. H. C. Forde 

 and Fleeming Jenkin of the Committee in the n.sual manner.' 



Table XI. gives Mr. H. A. Taylor's observations on his coils on the 

 assumption that Hockin's standard has not changed. 



Table XI. — -Assuming a Coil (Hockin's Standard) tested hy Electrical 

 Standards Committee ( 'M, No. 08) to he, as stated hy HocJcin, smaller 



ihanl B.A. Unit hy ^ ° / ^^ {three-hmdredihs per cent.) at 15°'5 C. The 

 Tahle slicivs the Resistance in terms of 1 B.A. Unit of other Standards 

 15°'5 C. at the dates given. 



1 (C. F. T.) copy called right) 



at 16°-1 Centigrade ) 



1 (No. 19) B.A. coil issued as) 



right at 15°-5 C. \ 



1 (No. 34) B.A. coil issued as j 



riglit at 15° 8 C. f 



10 (C. F. T.) copy called right 1 



atl5°-6C. I 



10 (No. 3) B.A. coil issued as | 



right at (?) / 



10 (No. 4) B.A. coU issued as 1 



right at 16°-0 C. ] 





03 



en 



30 s 



■"".SO 



I' rt . 



OJ --I 

 CO 



•99986 

 ■99980 

 1-00023 

 0-9992 

 10-0013 

 9-9995 



•99084 

 •90970 

 1-00023 

 9-9991 

 10-0013 

 99999 



Where the temperature of observation differs from i5°-5 C. the reductions to that 

 temperature are made by the temperature coefficients given. 



The evidence of a change is very small. The observations have lasted 

 over 14 years. For the first coil there would seem possibly to have been 

 a drop of abont '0001 between 1875 and 1879. The next coil may have 

 risen by as much and fallen again, while the third coil would seem to 

 have risen by -00015. The results for the ten ohm coils are much the 

 same. From the six coils, some of platinum silver, some of gold silver, 

 we conclude that there is certain evidence no change greater that 1 in 

 10,000 has occurred in the last fourteen years. 



The next table enables us to compare these coils with the standards at 



