ON STANDARDS FOR USE IN ELECTRICAL MEASUREJIENTS. 131 



such tLafc the square root of the time average of the square of its strength 

 at each instant in amperes is unity. 



12. That instruments constructed on the principle of the balance, in 

 which, by the proper disposition of the conductors, forces of attraction 

 and repulsion are pi-oduced, which depend upon the amount of current 

 passing, and are balanced by known weights, should be adopted as the 

 Board of Trade standards for the measurement of current, whether 

 unvarying or alternating. 



13. That the standard of electrical pressure should be denominated 

 the volt, being the pressure which, if steadily applied to a conductor 

 whose resistance is 1 ohm, will produce a current of 1 ampere. 



14. That the electrical pressure at a temperature of 15° Centigrade 

 between the poles or electrodes of the voltaic cell known as Clark's cell, 

 prepared in accordance with the specification attached to this report, may 

 be taken as not differing from a pressure of 1-434 volt by more than 

 one part in one thousand. 



15. That an alternating pressure of 1 volt shall mean a pressure 

 such that the square root of the time-average of the square of its value at 

 each instant in volts is unity. 



16. That instruments constructed on the principle of Lord Kelvin's 

 quadrant electi'ometer used idiostatically, and, for high pressures, instru- 

 ments on the principle of the balance, electrostatic forces being balanced 

 against a known weight, should be adopted as Board of Trade standards 

 tor the measurement of pressure, whether unvarying or alternating. 



(Signed) Courtenat Boyle. Kelvin. 



P. Cardew. W. H. Preece. 



Ratleigh. Gr. Carey Foster. 



R. T. Glazebrook. J. Hopkinson. 

 W. E. Ayeton. 



November 29, 1892. 



T. W. P. Blomefield, Secretary. 



Specification referred to in Resolution 10. 



In the following specification the term silver voltameter means the 

 arrangement of apparatus by means of which an electric current is 

 passed through a solution of nitrate of silver in water. The silver volta- 

 meter measures the total electrical quantity which has passed during the 

 time of the experiment, and by noting this time the time-average of the 

 current, or if the current has been kept constant the current itself, can 

 be deduced. 



In employing the silver voltameter to measure currents of about 

 1 ampere the following arrangements should be adopted. The kathode 

 on which the silver is to be deposited should take the form of a platinum 

 bowl not less than 10 centimetres in diameter, and from 4 to 5 centi- 

 metres in depth. 



The anode should be a plate of pure silver some 30 square centimetres 

 in area and 2 or 3 millimetres in thickness. 



This is supported horizontally in the liquid near the top of the solu- 

 tion by a platinum wire passed through holes in the plate at opposite 

 corners. To prevent the disintegrated silver which is formed on the 



