absolute

Part of the names of several electrical units, the absolute ampere, absolute ohm, absolute volt, etc., distinguishing them from the international ampere, etc.

The absolute practical system of units was defined by the First International Congress of Electricians (Paris, 1881) and included the volt, ohm, ampere, coulomb and farad. The joule, watt, and quadrant were added at the Second International Congress of Electricians (Paris, 1889). These units (as defined in the 19th century) have been obsolete since 1947.

In the British Association Report of 1863, “absolute” applied to a unit meant “that the measurement, instead of being a simple comparison with an arbitrary quantity of the same kind as that measured, is made by reference to certain fundamental units of another kind treated as postulates.” The word may have been first used in this sense by Gauss in an 1832 paper titled, “Intensitas vis magneticae terrestis in mensuram absolutam revocata.”

British Association for the Advancement of Science Report 1863, page 112.

sources

The precise meaning attached to the word “absolute” has been somewhat variable. It was originally used² as opposed to the word “relative.” It implied the use of units which depend upon units of other quantities taken as the fundamental quantities of a complete and self-consistent system. The object of an absolute system was to avoid complex coefficients in passing from one kind of measurement to another. The term has, however, been so used as to exclude gravitational units; that is, the fundamental units of an absolute system must be3 independent of variations in time and place. The actual use of the term “absolute” has been in connection with those systems which employ length, mass, and time as fundamental quantities. Thus, the “international” system of electric units is not spoken of as an absolute system, two of its fundamental quantities being electrical and only two mechanical. To designate a unit simply as an absolute unit is ambiguous, for that does not tell to what system the unit belongs. It is preferable to indicate the system specifically by such expressions as cgs, “practical” electromagnetic, etc.

The use of “absolute” as opposed to “relative” is familiar also in connection with measurements. Absolute measurements are those in which a physical quantity is measured in terms of those fundamental quantities of the system which enter into the dimensional formula of the physical quantity.

2. Report of the British Association Committee on Electrical Standards, 1863.

3. Webster. “The Theory of Electricity and Magnetism,” p. 100; 1897.

[U. S.] Department of Commerce.
Circular of the Bureau of Standards No. 60.
Electric Units and Standards.
Washington: U.S.G.P.O., 1916.
Pages 6 & 7.

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