The fourth book deals with the circle in its relations to inscribed and circumscribed triangles, quadrilaterals and regular polygons.
Owing to the small size of the experimental wire, the method is very quick and sensitive, and the apparatus can be set up in a few minutes when once the experimental quadrilaterals have been made.
37 The mensuration of earthwork involves consideration of quadrilaterals whose dimensions are given by special data, and of prismoids whose sections are D such quadrilaterals.
When dealing with maps not drawn on an equal area projection we substitute quadrilaterals bounded by meridians and parallels, the areas for which are given in the " Smithsonian Geographical Tables " (1894), in Professor H.
Quadrilaterals, hexagons, &c., all of which are rectilineal figures, a triangle is "differentiated" as having three sides.