# Constant

## Con"stant

, n. 1. That which is not subject to change; that which is invariable.[1913 Webster]

2.
*(Math.)* A quantity that does not change its value; -- used in countradistinction to
*variable*.

[1913 Webster]

3.
*(Astron.)* A number whose value, when ascertained (as by observation) and substituted in a general mathematical formula expressing an astronomical law, completely determines that law and enables predictions to be made of its effect in particular cases.

[Webster 1913 Suppl.]

4.
*(Physics)* A number expressing some property or condition of a substance or of an instrument of precision; as, the dielectric
*constant* of quartz; the collimation
*constant* of a transit instrument.

[Webster 1913 Suppl.]

5.
*(Computers)* a data structure that does not change during the course of execution of a program. It may be a number, a string, or a more complex data structure; -- contrasted with
*variable*.

[PJC]

**Aberration constant**,
*or*
**Constant of aberration**
*(Astron.)*, a number which by substitution in the general formula for aberration enables a prediction to be made of the effect of aberration on a star anywhere situated. Its value is 20.47. --
**Absolute constant**
*(Math.)*, one whose value is absolutely the same under all circumstances, as the number 10, or any numeral. --
**Arbitrary constant**, an undetermined constant in a differential equation having the same value during all changes in the values of the variables. --
**Gravitation constant**
*(Physics)*, the acceleration per unit of time produced by the attraction of a unit of mass at unit distance. When this is known the acceleration produced at any distance can be calculated. --
**Solar constant**
*(Astron.)*, the quantity of heat received by the earth from the sun in a unit of time. It is, on the C. G. S. system, 0.0417 small calories per square centimeter per second.
*Young.* [Webster 1913 Suppl.] --
**Constant of integration**
*(Math.)*, an undetermined constant added to every result of integration.

[1913 Webster +
Webster 1913 Suppl.]

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Tue 11th December 2018