An absolute determination of the ampere

Abstract

The current balance originally used by Rosa, Dorsey, and Miller in 1911 has been somewhat modified and used to determine the absolute value of the ampere. The value in absolute amperes of the current in the coils of the balance was determined from the measured constants of the coils and the electromagnetic force between them. The most important constant which could be directly measured was the ratio of the radii of the coils, which was measured by an electrical method. The values obtained on four sets of coils indicated that there was no error in the measurement of the ratio of the radii greater than three parts in a million.

Calorimetric determination of the heats of combustion of ethane, propane, normal butane, and normal pentane

“…Recent experimental work in this Bureau (13) on the relation between the international and the absolute units of current and resistance indicates the relation between the absolute joule and the international joule, derived from standards maintained at this Bureau, to be 1 international (Bureau of Standards) joule = 1.00032 absolute joules. But for the sake of consistency the relation which has heretofore been used for converting the data obtained in the thermochemical laboratory of the Bureau of Standards will be used in the present and succeeding papers, until such time as the relation between the absolute and the international joule will be fixed by international accord.…”

An absolute determination of the ampere, using helical and spiral coils

“…In the previous investigations the sources of error have been discussed in detail [2,8]. In general the same discussion applies to this determination.…”

“…Spiral and helical coils meet the last condition more satisfactorily than the multilayer coils of wire which were used in an earlier determination [8]. Spiral fixed coils, a spiral moving coil, and a helical moving coil have already been described [2].…”

Standard cells :

“…(2) In terms of measurements with current balances and standard resistorsin 1934 Curtis and Curtis [40] using a current balance originally used by Rosa, Dorsey, and Miller [41] found that 1 NBS international ampere ( (4) In terms of "neutral" and "acid" cellsthe difference between the average emfs of the "neutral" and "acid" cells in the National Reference Group of Standard Cells has increased by 8.5 fxV in 26 years, with the increase being only 1.0^tV during the last 10 years [42]. This comparison was made for 7 "neutral" and 11 "acid" cells, or for cells of " These results published by Vinal [34] were reported to the fifth decimal and Since the emfs of "neutral" and "acid" cells have remained relatively constant during the last 10 years the earlier drift in their difference may be attributed to an aging effect exhibited by the "acid" cells (the "neutral" cells were 26 years old at the start of the comparison between the "neutral" and "acid" cells).…”