156 REPORT— 1891. 



3. That the standard of electrical resistance should be denominated 



the ohm, and should have the value 1,000,000,000 in terms of 

 the centimetre and second. 



4. That the resistance offered to an unvarying electric current by 



a column of mercury of a constant cross sectional area of one 

 square millimetre, and of a length of 106'3 centimetres at the 

 temperature of melting ice may be adopted as one ohm. 



5. That the value of the standard of resistance constructed by a 



committee of the British Association for the Advancement of 

 Science in the years 1863 and 1864, and known as the British 

 Association unit, may be taken as "9866 of the ohm. 



6. That a material standard, constructed in solid metal, and veri- 



fied by comparison with the British Association unit, should 

 be adopted as the standard ohm. 



7. That for the purpose of replacing the standard, if lost, destroyed, 



or damaged, and for ordinary use, a limited number of copies 

 should be constructed, which should be periodically com- 

 pared with the standard ohm and with the British Associa- 

 tion unit. 



8. That resistances constructed in solid metal should be adopted 



as Board of Trade standards for multiples and submultiples of 

 the ohm. 



9. That the standard of electrical current should be denominated 



the ampere, and should have the value one- tenth (O'l) in 

 terms of the centimetre, gramme, and second. 



10. That an unvarying current which, when passed through a 

 solution of nitrate of silver in water, in accordance with the 

 specification attached to this report, deposits silver at the 

 rate of 0001118 of a gramme per second, may be taken as a 

 current of one ampere. 



11. That an alternating current of one ampere shall mean a cur- 

 rent such that 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 produced, 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 alter- 

 nating. 



13. That the standard of electrical pressnre should be denomi- 



nated the volt, being the pressure which, if steadily applied to 

 a conductor whose resistance is one ohm, will produce a cur- 

 rent of one ampere. 



14. That the electrical pressure at a temperature of 62° F. between 

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

 cell, may be taken as not differing from 1-433 volts by more 

 than an amount which will be determined by a sub-com- 

 mittee appointed to investigate the question, who will prepare 

 a specification for the construction and use of the cell. 



15. That an alternating pressure of one 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 nnity. 



