ON STANDARDS FOR USE IN ELECTRICAL MEASUREMENTS. 



67 



Cambridge. It will be noticed at once that relatively to the Cambridge 

 standards the coils have all fallen. 



Table XTI. 



Let us take fir.st Hockin's standard "^S* 68. Using Taylor's tempera 



ture coefficient we find as its present valne — the mean of the two given 

 in the last column — at 1.5°-5, -99901. It has therefore fallen relatively 

 to the Mean B. A. Unit by '00069, practically the same fall as that found for 

 all the other platinum silver coils examined. The coil C.F.T. (the first 

 coil in Table XI.) will also clearly have fallen by the same amount. 

 Similarly with the ten unit platinum silver coil '^_ 69 ; it has fallen from 



10 to 9-9940, or by '006, nearly the same percentage ; and since, accord- 

 ing to Table XL, the coils have not changed relatively to each other and 

 to the gold silver coils by more than one-sixth of this amount since 1874, 

 there is some probability that the change, if it has taken place at all, 

 occurred between 1867 and 1874. It will be remembered that we arrived 

 at a similar conclusion with regard to G. The difference between the 



values of ^ 68, found by myself in 1887 and 1882 as recorded in the 



two last lines of Table XII., arises from the fact that in 1887 the coil was 

 compared with F, and in 1888 with Flat and G. In making the calcu- 

 lation it was assumed that the values of F, Flat, and G in terms of the 

 Mean B.A. Unit had remained unchanged since Fleming's time. The 

 results of our comparisons given in Tables IV., Y., &c., would, as has been 

 said, point to a slight rise in F of possibly as much as -0001, and this 



would reconcile the two values for 1 H or ^ 68. As regards the gold 



silver coils Nos. 19 and 34, if we take the value as issued, the one has 

 fallen by -00111, the other by -00037. We must remember that the tem- 

 perature coefficients for these coils are much greater than for the platinum 

 silver coils. 



If, however, we compare the values as issued with those found by 

 Taylor in 1875 — Table XL, column five — we find that while Xo. 19 was 



