Abstract
The ampere has been determined by means of the Ayrton-Jones current balance of the National Physical Laboratory. The result shows that the unit of current maintained at the Laboratory by standard resistors and standard cells exceeds the ampere by 15 in 106, with a probable error of 4 in 106. From this figure and a previous measurement of the precessional frequency of protons, it is deduced that the gyromagnetic ratio of the proton in water, uncorrected for diamagnetism, is 2.675 13 × 108 C/kg with a total probable error of 5 in 106.