ON PRACTICAL STANDARDS FOR ELECTRICAL MEASUREMENTS. 41 



And whereas in the said Schedule the limits of accuracy attainable 

 in the use of the said denominations of standards are stated as 

 follows : — 



For the Ohm within one hundredth part of one per cent. 



For the Ampere within one tenth part of one per cent. 



For the Volt within one tenth part of one per cent. 



And whereas, at an International Conference on Electrical Units 

 and Standards held in London in the month of October, 1908, the 

 International Electrical Units corresponding with the said denomina- 

 tions of standards were defined as follows : — 



The International Ohm is the resistance offered to an unvarying 

 electric current by a column of mercury at the temperature of melting 

 ice 14'4521 grammes in mass of a constant cross sectional area and of 

 a length of 106'300 centimetres. 



The International Ampere is the unvarying electric current which, 

 when passed through a solution of nitrate of silver in water, deposits 

 silver at the rate of O'OOl 11800 of a gramme per second. 



The International Volt is the electrical pressure which when steadily 

 applied to a conductor whose resistance is one International Ohm will 

 produce a current of one International Ampere. 



And whereas it has been made to appear to the Board of Trade to 

 be desirable that the denominations of standards for the measurement 

 of electricity should agree in value with the said International Electrical 

 Units within the said limits of accuracy attainable ; 



And whereas the denominations of standards made and duly verified 

 in 1894 and set forth in the Schedule to the said Order in Council have 

 been again verified ; 



And whereas the Board of Trade are advised that the said denomina- 

 tions of standards agree in value with the said International electrical 

 units within the said limits of accuracy attainable, except that in the 

 case of the Ohm the temperature should be 16°"4 C. in place of 15°'4 C. 

 as specified in the Schedule to the said Order in Council ; 



And whereas it has been made to appear to the Board of Trade that 

 the said denominations of standards should be amended so that the 

 aforesaid exception may be remedied; 



Now, therefore, His Majesty, by virtue of the power vested in Him 

 by the said Act, by and with the advice of His Privy Council, is pleased 

 to revoke the said Order in Council dated the 23rd day of August, 1894, 

 and is further pleased to approve the several denominations of standards 

 set out in the Schedule hereto as denominations of standards for the 

 measurement of electricity. Almeric Fitzeoy. 



' Schedule above referred to. 



' I. Standard of Electrical Resistance. 



' A standard of electrical resistance denominated one Ohm agreeing 

 in value within the limits of accuracy aforesaid with that of the Inter- 

 national Ohm and being the resistance between the copper terminals of 

 the instrument marked " Board of Trade Ohm Standard Verified, 1894 

 and 1909," to the passage of an unvarying electrical current when the 



