CONSTANTS OF NATURE. A term ap plied to various unchangeable quantities that are found to be characteristic of natural phe nomena or relations. The propagation of light through space takes place invariably at the rate of 186,770 miles per second, and hence the velo city of light may be referred to as a constant of nature. The period of rotation of the earth on its axis may be considered as another con stant of nature, although, strictly speaking, it is subject to slight variation. The atomise weights of chemistry—i.e. the smallest relative combining weights of the elements—furnish an other example of important constants of nature —important because they permit. of expressing the composition and reactions of all substances in a simple and useful form. The electrolytic equivalents—i.e. the weights of elements deposit ed in the electrolysis of their compounds by a unit current in one second—are likewise con stants characteristic of the several chemical ele ments.
In choosing the units of precise measurement, which form the basis of all calculations in pure each applied science, it is necessary to employ the constant quantities of nature. For example. the second, which is the unit of time generally used at present. is defined in terms of the time of a complete revolution of the earth on its axis. As thus defined. however, the unit is not quite perfect; the time of a revolution of the earth on its axis is subject to slow variation, and hence the dn•ation of the second, referred to that time, must likewise be slowly changing. With a view to establishing a more perfect, unit of time, scientists have proposed to adopt as its basal constant of nature the period of vibration of an atom emitting light of a given wave-length—an interval of time that is believed to be absolutely constant.
The laws of science are generally expressed in the form of mathematical equations whose num bers and terms represent the eonstant as well as the variable factors of typical natural pheno mena. Thus• the variation of volume under
variable conditions of temperature and pressure. which is characteristic of all bodies, is in the case of perfect gases subject to laws that are usually expressed by the equation PV = RT, in which P stands for pressure, V for volume, and T for the absolute temperature. If. in experi menting with different gases. we should employ such quantities of them as would, under the same conditions of pressure and temperature, occupy equal volumes. we would find that while the pressure and temperature might subsequently be changed, the factor It would remain constant and the same for all gases, irrespective of their chemical nature: that is to say, the product of the pressure and volume (PV), divided by the absolute temperature (T). would yield invaria bly the same number. That number (II). called 'the gas constant,' is therefore obviously charac teristic of the interdependence of pressure, vol ume, and temperature, in all gaseous matter; and being so general, it has great importance in both pure and applied science. Thus, the con stants of nature characterize natural phenomena and enter into all the mathematical laws of science.
Consult: Lupton. Everett, C. G. S. System of Units (London. 1891) ; Landoll, and Bornstein, Physikalisch-eheinische Tab('ilea (Berlin, 1893) ; Clarke, The Constants of Nature (5 parts, Sin it h sonia Miscellaneous Collections. Washington, 1873-88). Some of the constants of nature may of course he found in any scientific text-book. See also CALCULUS; C. G. S. SYSTEM.