Absolute System of Units

ABSOLUTE SYSTEM OF UNITS, a rationally constructed system in which the units of all quantities are reduced to three fundamental ones. The principle of constructing such a system is as follows. Each newly introduced concept is given a quantitative definition by means of a formula connecting the new quantity with previously established ones. Thus, work (A) is defined as a quantity proportional to force (f) and the path (s) traversed by the point of application. Therefore, A = k·f·s, where k is a constant coefficient whose numerical value depends on the choice of units entering into the formula. Until one commits to a specific value of this coefficient, all quantities entering into the formula can be measured in any units; for each system of units, k will have its own special value. But in constructing an absolute system of units, the unit of the newly introduced quantity is chosen so that always k = 1. Obviously, this can be done in only one way, namely, in this case, for example, it is necessary to adopt as the unit of work the work of a force equal to 1 over a path equal to 1, since then 1 = 1·1·1; k = 1. Thus, having the units of force and length, the unit of work is fixed. Proceeding similarly with any newly introduced quantity, a logically flawless system of units can be constructed. The three fundamental units can be chosen quite differently, provided that the quantities measured by them are mutually independent. In science, however, a definite system is generally accepted: the so-called C.G.S. system, in which the fundamental units taken are: the unit of length—the centimeter (C), the unit of mass—the gram (G), and the unit of time—the second (S). At present, it has been agreed to give the fundamental definitions to the fundamental units as follows: 1) the centimeter is one-hundredth of the distance at 0° between the marks of the standard preserved in the International Bureau of Weights and Measures in Sèvres (France) and called the international meter; 2) the gram is one-thousandth of the mass of the platinum standard preserved in the same Bureau and called the international kilogram; 3) the second is ¹/_86,400 part of the mean solar day. The first two standards are very close to quantities encountered in nature, namely, the meter is 0.0856 mm shorter than one ten-millionth of the Paris meridian quadrant, and a kilogram of water is equal to the mass of 1.00005 cubic decimeters of water at 4°. But the initial idea of connecting the fundamental units with quantities encountered in nature has now been abandoned as unfeasible. Despite the entire scientific elegance of the absolute system of units, absolute units are practically often inconvenient to use: they are either too small or too large. Therefore, in technology and in life, one very frequently uses not the absolute units themselves, but their decimal derivatives: instead of the centimeter—the meter = 100 cm, instead of the erg (the absolute unit of work)—the joule = 10⁷ ergs, and so on.