The Practical Draughtsman's Book of Industrial Design; Forming a Complete Course of Mechanical, Engineering, and Architectural Drawing

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1853 Excerpt: ...it is an exemplification which cannot be omitted; and its chief use is to show, that The shadow cast by a straight line upon a plane surface is invariably a straight line; and, consequently, it is sufficient to determine its extreme points, in order to obtain the entire shadow in any one plane. Thus, the straight line, E' C', casts a shadow upon the plane facet, /c, which is represented by the straight line, ec It is further obvious, that The shadow cast upon a plane surface, by any line parallel to it, must be parallel to that line. Thus, the straight line, E' a', of the larger prism, b, being parallel to the plane facet, f g', of the prism, A, casts a shadow upon the latter, which is represented by the straight line, fg, parallel to the line, F G, the vertical projection of the edge, F' G'. It is not, however, the same with the portion, e/, because the corresponding portion, E' F', of the edge of the larger prism, is not parallel to the facet, /'e'. SHADOW CAST bY A PRISM UPON A CYLINDER. 285. Figs. 9 and 9 represent vertical projections, at right angles to each other, of a portion of an iron rod, A, surmounted by a concentric head, B, of a hexagonal base. The main object of this diagram is to show, that When a right cylinder is paralleI, or perpendicular, to a plane of projection, any straight line, which is perpendicular to the axis of the cylinder, and parallel to the plane of projection, casts a shadow upon Vie cylindrical surface, which is represented by a curve, similar to the cross section of such surface. If, therefore, the cylinder is of circular base or cross section, as we have supposed in the present case, the shadow cast upon it will be a portion of a circle, of the same radius as the cylinder. Thus, the straight line, D' F', situated in ...