136 REPORT— 1894. 



In the case of copper ' with increase of purity there is a decrease in 

 the difference in resistance between annealed and hard-drawn wires. 

 With silver the reverse is the case. 



Silver I. — Difference 75 



„ II. — Difference 77 



„ III.— Difference . . . - . . .107 



The value that I obtained for the hard-drawn wire is very nearly the 

 same as that given by Matthiessen, but he obtained a greater decrease in 

 resistance on annealing. He states ^ that for different pieces of the same 

 wire there was a variation of from 6 to 10 per cent. ; so that the dif- 

 ference between his value and that which T have obtained for a sample of 

 pure silver is not greater than might be expected. 



The considerable variation in all the values given above makes it clear 

 that the values of the specific resistance depend not simply on the purity 

 of the material, but on a number of other factors, which will be different 

 in the cases of different wires of the same material, and that therefore 

 we cannot expect to attain to any great degree of accuracy in the 

 determination of specific resistances as distinguished from the accurate 

 measurement for some particular wire. 



APPENDIX VII. 



Final Report of the Electrical Standards Committee of the Board of Trade. 



To the Right Hon. James Bryce, M.P., 



President of the Board of Trade. 



Since the date of our last Report the Board of Trade have laid before 

 us a resume of the action of the International Electrical Congress held 

 in Chicago in August 1893 to determine the units of electrical measure- 

 ment. We were also informed by the Boaixl of Trade that her Majesty's 

 Govei-nment had been invited by the United States Ambassador in 

 London to take steps to adopt the recommendations of the Congress. 



These recommendations, so far as they refer to the units of electrical 

 resistance, electrical current, and electrical pressure, are substantially the 

 same as those suggested for adoption in our previous Reports. 



We see no reason f(jr further delay in the legalisation of standards of 

 the above-mentioned units, and we have prepared and attach a revised 

 Draft Order in Council,^ which we advise may be submitted for her 

 Majesty's gracious approval. 



The accompanying notes ■* to the specification for the Clark's cell have 

 been communicated by Mr. Glazebrook, and will be found of great 

 assistance in the preparation of this form of cell. 



(Signed) Courtenay Boyle. Kelvin. 



Francis J. S. Hopwood. P. Cardew. 



W. H. Preece. Rayleigh. 



G. Carey Foster. R. T. Glazebrook. 



J. HoPKiNsoN. W. E. Ayrton. 



T. W. P. Blomefield, Secretary. 

 August 2, 1894. 



' B.A. Itep , 1800, p. 126. == Phil. Trans., 18C2, p. 7 



' The Order in Council is printed in the form in which it has since received her 

 Majesty's approval. * For the notes see p. 141. 



