The Practical Draughtsman's Book of Industrial Design, and Machinist's and Engineer's Drawing Companion (Paperback)

This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1854 edition. Excerpt: ...to the line, F G, the vertical projection of the edge, F' G'.. It is not, however, the same with the portion, ef 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 9a 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 parallel, 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 the cylindriccd 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 a plane, at right angles to the axis of the cylinder, A, and being, at the same time, parallel to the vertical plane, casts a shadow upon the cylinder, which is re presented by the portion, c ef, of a circle, the centre, o, of which is obtained by drawing through the point, o, a line, o I, representing the ray of light, and extending to the prolongation of the edge, D' F', The line, 0 I, cuts the circumference of the cylinder in the point, i, which is squared over to i, upon the other projection, H i, fig. 9, of the ray, o I. The lower point, c, is obtained from the upper one, i, being symmetrical with reference to the axis of the cylinder. The ray, H i, being continued to the axis, cuts it in the point, d, which is, ...