GRAPHIC METHOD, a pictorial method of representing statistics by lines. Force, mo tion or any other physical quantity, such as temperature, atmospheric pressure or baro metric height, electric potential, etc., may be represented by straight lines. Graphic methods are largely employed in physical investigations as aids to calculation, and for the purpose of exhibiting the nature of the law according to which some phenomena vary. The principal use of this method is to show the mutual varia tions of two quantities. This we will illustrate by a particular example. Suppose a table is drawn up, in one column of which are the months of the year, and in the other the cor responding average temperatures of the air, at some particular place, during these months (the average temperature for each month being the mean of the daily temperatures). Let two lines, OX and OY, be drawn from 0, one horizontally, the other vertically; let the suc cessive months of the year be represented on any convenient scale along OX, and let tem perature be measured along OY, also on a con venient scale. Corresponding to each month in
the year there will be a length along OX, and to each temperature there will correspond a point on OY. At the middle point correspond ing to each month draw perpendicular to OX a line representing the temperature on the scale of OY. A series of lines will thus be obtained, through the upper ends of which there may be drawn, freehand, a smooth curve. The points on the curve in the figure represent the upper ends of these lines. Other graphic methods in volve the use of polar, logarithmic and other varieties of co-ordinates. (See GEOUETRY, ANALYTIC). A general glance at such a curve will reveal certain features regarding the tem perature of the whole year; at what dates maxima and minima occurred; when the tem perature rose or fell quickest, and so on.