VARIABLE

, in Geometry and Analytics, is a term applied by mathematicians, to such quantities as are considered in a Variable or changeable state, either increasing or decreasing. Thus, the abscisses and ordinates of an ellipsis, or other curve line, are Variable quantities; because these vary or change their magnitude together, the one at the same time with the other. But some quantities may be Variable by themselves alone, or while those connected with them are constant: as the abscisses of a parallelogram, whose ordinates may be considered as all equal, and therefore constant. Also the diameter of a circle, and the parameter of a conic section, are constant, while their abscisses are Variable.

Variable quantities are usually denoted by the last letters of the alphabet, z, y, x, &c; while the constant ones are denoted by the leading letters, a, b, c, &c.

Some authors, instead of Variable and constant quantities, use the terms fluent and stable quantities.

The indefinitely small quantity by which a Variable quantity is continually increased or decreased, in very small portions of time, is called the differential, or increment or decrement. And the rate of its increase or decrease at any point, is called its fluxion; while the Variable quantity itself is called the fluent. And the calculation of these, is the subject of the new Methodus Differentialis, or Doctrine of Fluxions.

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Entry taken from A Mathematical and Philosophical Dictionary, by Charles Hutton, 1796.

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TYSHAS
VACUUM
VALVE
VANE
VAPOUR
* VARIABLE
VARENIUS (Bernard)
VARIATION
VARIGNON (Peter)
VAULT
VEADAR