"Descriptive geometry has two objects: the first is to establish methods to represent on drawing paper which has only two dimensions,-namely, length and width,-all solids of nature which have three dimensions,-length, width, and depth,-provided, however, that these solids are capable of rigorous definition. The second object is to furnish means to recognize accordingly an exact description of the forms of solids and to derive thereby all truths which result from their forms and their respective positions."