A panorama is a picture drawn on the interior surface of a large cylinder, representing the objects that can be seen from one station, when the observer directs his eye successively to every point of the horizon. A picture drawn on a vertical plane in the usual way includes only that portion of the sphere of vision that can be seen from one point opposite to the picture, without turning the eye; this portion may comprehend about thirty degrees of the horizon, because the field of distinct vision when the eye remains unmoved is concluded in a cone the angle at the apex of which does not exceed thirty degrees. There are compositions comprehending the visible hemisphere, and sometimes nearly the whole sphere of vision; and in these, one connected scene is represented on the interior surfaces of a polyhedron, or of a curved solid, the point of sight being in the centre of the polyhedron, and the eye being turned round on its centre, to each of its surfaces, in order to view the whole scene. Of this kind are the gnomonic projection of the sphere on the interior surfaces of a cube, and several pictures, in which one connected subject is represented on the ceiling and the sides of a room; such as the picture of Jupiter fulminating the giants, by Julio Romano, on the walls and hemispherical ceiling of a round room in the Palazzo del T, at Mantua; and the architectural representations and ornaments in Raffaele's Loggia in the Vatican. Objects are also sometimes projected on the interior surface of a sphere, the eye being placed in the centre; as in a large hollow sphere with the constellations, which was constructed at Panormo Pembroke College, Cambridge. These projections, where the eye, remaining in the point of sight, is turned round Pantenus, on its centre to view the different parts of the picture, are formed on the same principle as the panorama.

The cylindrical surface is the most convenient for panoramas of landscapes; and the specific employment of a large cylindrical surface for representing the landscape of the whole circle of the horizon, is the invention of Mr Barker, who brought the panorama into use, and still continues to exercise his art. The cylinder on which the panorama is painted is commonly about sixty feet in diameter. The projection or perspective of a panorama is formed by imaginary lines drawn from different points of the surrounding objects, to the point of sight in the axis of the cylinder. The intersections of these lines with the cylindrical surface form the corresponding points in the panoramic picture. Where the picture is projected on a plane, as in common perspective, and in the gnomonic projection of the sphere, the cones formed by imaginary lines or rays passing from the point of sight to the different objects are cut by the plane of the picture; consequently, the sections being formed by a plane, are curves, of which the curvature is always simple. In the perspective of the panorama, where the picture consists of the intersection of the cones of rays by a cylinder, these intersections are, in many of the cases, doubly curved curves. When the picture of a straight line, which is neither parallel to the horizon nor to the axis of the cylinder, is drawn on the cylinder of the panorama, the picture of the line is part of an ellipse, because the oblique section of a right cylinder, by a plane passing through the axis, is an ellipse; when the cylinder is developed and unrolled on a plane surface, this ellipse becomes the curve called the sinal curve. The projection of lines on the interior surface of a cylinder is also employed in drawing Mercator's charts. But in the projection of the panorama, the field extends only a few degrees above and below the horizon, whereas, in the projections of the sphere, the field extends many degrees on each side of the plane, which is at right angles to the axis of the cylinder. In drawing a panorama, as well as in drawing a picture on a plane, the horizontal angles between different objects may be observed by a plane table or theodolite; and the elevation of the objects above the horizon, or their depression, may also be observed by the theodolite. The horizontal angles are to be laid down by setting off on the graduated horizon of the cylindrical picture the number of the degrees observed; the vertical angles on the cylinder are the tangents of the angles observed, the radius being the semidiameter of the cylinder. (a.b.)