Olaus Magnus Friedrich Henrici

“ For the construction of the shadow of points it is convenient first to draw a perpendicular from the point to the ground and to find its shadow on the ground. But the shadows of verticals from a point at infinity will be parallel;hence they have in perspective a vanishing point L; in the horizon. To find this point, we draw that vertical plane through the eye which contains a ray of the sun. This cutsthe horizon in the required point L; and the picture plane in a vertical line which contains the vanishing point of the sun's rays themselves. ”

“ The perspective of any curve is in general a curve. The projection of a conic is a conic, or in special cases a line. The perspective of a circle mav be any conic, not necessarily an ellipse. Similarly the perspective of the shadow of a circle on a plane is some conic. ”

“ The perspective of a iiorizontal plane from the picture to the line at infinity occupies in the picture the space between the Iine where the plane cuts the picture and the horizon, and this space is the greater the farther the plane is from the eye, that is, the farther its trace on the picture plane lies from the horizon. ”