ON STANDABDS FOR USE IN ELECTRICAL MEASUREMENTS. 137 



The Board of Trade Committee recommended for adoption the values 

 -9866 and 106-3. 



The specific resistance of mercury in ohms is thus 



•9407 X 10-^ 



Also 1 Siemens unit = "9407 Ohm 



= -9535 B.A.U. 

 1 Ohm =1-01358 B.A.U. 



The results found by Lord Eayleigh were reduced by the use of the 

 value for the specific resistance of mercury in B.A. units found by him. 

 If instead we use the value •9585, the mean of the best determinations, 

 we have, as in the table, for the length of the mercury column having a 

 resistance of 1 ohm the values 106'27 and 106'31. At the meeting of the 

 Committee M. Guillaume stated that a correction should be made to M. 

 Wuilleumeier's value, which would raise it to 106;31. This arose from 

 some uncertainty as to the correction required to the resistance of mercury 

 for change of temperature on which M. Guillaume had been working 

 lately. Taking these corrections we arrive at 106'31 as the mean of the 

 above. 



2. The Electrolysis of Silver. 



The following values have been found for the mass of silver deposited 

 from a solution of silver nitrate in one second by a current of 1 ampere : — 



Mascart, ' J. de Physique,' iii. 1884 .... -0011156 



Eayleigh, ' Phil. Trans.,' ii. 1884 .... -0011179 



Kohlrausch, ' Wied. Ann.,' sxvii. 1886 . . . -0011183 



T. Gray, ' Phil. Mag.,' sxii. 1886 . . about -001118 



Potier et Pellat, ' J. de Physique,' ix. 1890 . -0011192 



Dr. Schuster has shown ('Proc. R.S.,' 1. 1892) that the amount of 

 silver deposited when the voltameter is in a vacuum is about '04 per 

 cent, greater than when it is in air. 



3. Clark Cells. 



The following values have been found for the E.M.F. of a Clark cell 

 at 15° C. They have been reduced from those given in the original papers 

 on the supposition that 1 B.A.U. :='9866 ohm, and that the mass of 

 silver deposited per second per ampere is •001118 gramme : — 



Eayleigh, 'Phil. Trans.,' ii. 1884 .... 1-4345 Volt 



Carhart 1-4340 „ 



Kahle, ' Zeitschrift fiir Instrumentenkunde,' 1892 . 1-4341 „ 



Glazebrook and Skinner, 'Proc. E.S.,'li. 1892 . 1-4342 „ 



A comparison has been made between the standards of the Association 

 and the Berlin standards through a Clark cell and a resistance coil 

 belonging to Dr. Schuster. By the kindness of Dr. von Helmholtz the 

 Secretary is able to communicate the results of a direct comparison 

 between the two sets of standards to the meeting (see Appendix VIII.). 



