34 KEPORT— 1903. 



assigned to tliem by Fleming in 1881. The conclusion is also drawn in the 

 same report that, with the exception of the platinum-iridium coils A and 

 B, no really certain variations could be traced in the other coils between 

 the results of Matthiessen and Hockins's comparisons in 1864 and 1867, 

 those of Chrystal in 1876, Fleming in 1881, and the present Secretary ' in 

 1888. A postcript to the Report for 1888 recorded, however, an appre- 

 ciable change in the coil F in the autumn of that year. 



In Appendix I. Mr. Smith starts with the values given in the 1888 

 Report, which are, as nearly as we can tell, the original values of the 

 coils. 



Changes in the three standards F, G, H have already been recorded 

 in previous Reports (1890 and 1892). The standard coil Fiat remained 

 unchanged in value until 1901-1902. Between the observations recorded 

 in these years it increased in resistance by 17 x 10""'^ B.A.U., and has not 

 varied since. 



The alterations in the other coils since the comparisons in 1888 have 

 been as follows : — 



F. + 97xlO-''B.A.U. 



G . + 33 X 10-5 ^^ 

 H. + 18x10-5 „ 



It should however be noted that, while between 1888 and 1890 the 

 change in F was +64x10"* B.A.U., that in G was —27 x 10"*, and 

 in H —13x10-^. Since 1890 the same coils changed by +33x10"* 

 + 54 X 10"*, and +31 x 10"* B.A.U. respectively, while between 1901 and 

 1902 Flat, as has already been stated, rose by 17 X 10"* B.A.U. 



It is not easy to trace the causes of these changes. In the case of Flat 

 the observations in 1901 were made at Kew, those in 1902 at Bushy 

 House, and the change may in some way be connected with the removal 

 of the coils. The changes in F, G, H first showed themselves after the 

 coils had been subject to a very low temperature, and may have been 

 started by strains due to this. 



Appendix I. gives the details on which these various statements are 

 based. It appears also from the same Appendix that the new platinum- 

 silver ohm standards of the Association have retained their values since 

 1898 practically unchanged. 



The comparison between the standards of the Association and those 

 of the Reichsanstalt leads to the result that the unit of the Association 

 (No. 5 of those defined above) is less than that of the Reichsanstalt 

 (No. 6) by -000105 ohm. This result is deduced (Table IX. of Appendix I.) 

 from a series of extremely concordant measures on coils of value 0-1, 1, 

 10, 100, 1,000, and 10,000 ohms ; thus both the unit and the multiple 

 coils agree in giving tlie same difference between the Reichsanstalt and 

 ourselves. 



By the kindness of Mr. Trotter a comparison has been made between 

 the Board of Trade unit and those of the Association, with the result 

 that, as deduced from the unit coils, the Board of Trade unit is less than 

 that of the Association by -00006 ohm. This result, however, is not 

 confirmed by a comparison of a 1,000-ohm coil belonging to the Associa- 



' It is possible that coil JF is an exception to this statement. 



