Pocketbook of Useful Formulæ and Memoranda
for Civil and Mechanical Engineers

388 moleswortii’s pocket-book Centre of Gbavity. (By Graphic Construction.) Divide the section into any convenient layers and construct a polygon of forces as follows With any convenient scale set out on a horizontal line lengths corresponding with the area of each layer; assume any convenient point C, and draw lines from the lengths thus set out radiating to C. Then lines drawn parallel to these radiating lines, as shown in the diagram, intersecting the horizontal lines that pat-s through the centre of gravity of each layer respectively form the polygon of forces, and the intersection of the lines a f gives the horizontal line of the centre of gravity of the layers. The centre of gravity of any number of bodies A B D E may be found by constructing a polygon of forces in a similar manner for horizontal qs well as for vertical forces, the Inter- section of the two lines if polygons giving the centre of gravity at G. FOR VERTICAL FORCES. FOK HORIZONTAL FORCES.