WEIGHT

In Physics, that property of bodies in virtue of which they tend towards the centre of the earth. In this sense, weight is synonymous with gravity. See Gravity. Weight, in Mechanics, denotes the resistance to be overcome bya machine, whether in raising, or sustaining, or moving a heavy body. The force applied to the machine for this purpose is called the moving power; and where the equilibrium subsists, the difference between the weight and the moving power is the purchase of the machine. In all cases of equilibrium by the intervention of machinery, if the machine be put in motion by a small additional force, the space pa ed over by the moving power will 'je greater than that pa ed over by the weight, in proportion as the weight is greater than the moving power; or the product of the weight by its velocity will be r(;ual to the product of the moving power by its velocity. See Momentum, Virtual Velocity. Weight, in Experimental Philosophy and Commerce, is the measure of the force by which any body, or a given portion of nny substance, gravitates to the earth. The proce by which this measure is obtained is called weighing; and when required, as in many philosophical experiments, to be performed with great accuracy, is a tedious and delicate operation. See Balance. The measurement of weight, like that of extension, consists in the comparison of the thing to be measured with some conventional standard. But it is impo ible to fix such a standard by written law or oral description; for it is impo ible to communicate by words, and without reference to a sensible object, any adequate idea of a pound-weight, or foot-rule. Standards of linear measure, not accurately defined indeed, but having an average value sufficiently well known for the rude purposes of mankind in the early rtages of society, were furnished by the different parts of the human body; hence the measures foot, cubit, span, pace, fcc. (See Measures.) But the method of comparing the weights of bodies does not suggest itself so readily to the mind as the comparison of linear dimension, and is not so [s. 1345]