SIDE. In modern mathematics this term means nothing but one of the lines which bound a figure, extending from one angle or corner to the next. The Latin word lefties, of the same signification, is pre served in composition : thus a figure of three sides is trilateral ; of four, quadrilateral ; of five, quinquilateral; and so on. At the intro duction of algebra, the same geometrical analogies by which a number multiplied by itself was called a square, procured for the number itself the name of ride; thus 7 being the aide, 49 was the square; and the same of the cube, triangular polygonal, and pyramidal numbers. [NUMBERS, APPELLATIONS 011 In common language the side is a vague term, implying only "part, with a notion of relative position;" it is also differently used in and out of composition. First we have the inside and outside; then, with reference to either of these, we have sides before and behind, above and below, right and left. The first pair is defined by reference to the spectator, the second by the direction of gravitation; but the third, with reference to which the term side is most frequently used, cannot be defined by the mathematician. The anatothist will say, that in the
human body, the right side is that on which the heart is not, and the left side that on which it is, and there is no other definition. In every cue in which the terms right and left are applied, there is a reference to the position of the human body. Thus the right wing of an army means that which is towards the right hands of those in the centre; as soon as a retreat commences, the names of the right and left wings are changed. The right bank of a river is by convention named on the supposition that the person who names it is looking down the stream, or seeing the water flow from him. Perhaps some may doubt whether the superior and inferior parts, or the anterior and posterior, are in our language properly called sides; these we must remind that the words fore-side and back-side are very good English ; and that in the phrase upside-down we see the remains of the corresponding phrases up-side and down-side.