SCIOPTIC BALL is a globe of wood about 5 inches diameter, with a cylindrical perforation 2i inches diameter passing centrally through it, and having at one extremity of the perforation a glass lens The globe or ball is, by means of screws, fixed in a socket, which is made in a board about 8 or 10 inches square, in such a manner that while it cannot fall out, it is capable of being turned on its centre, to a small extent, in any direction.
The board being screwed to a window-shutter, or to the vertical face of a building in which an aperture has been made for the reception of the globe, the rays of light from external objects, after being refracted in the lens, form pleasing imagers of those objects on the opposite wall of the apartment, or on a white screen placed in a vertical position to receive the light; the apartment being darkened in order that the images may be distinct. The images on a vertical screen being in verted, two arms generally project from the board, within the room, and carry a piano mirror which turns on an axis so as to allow the rays of light, after passing through the lens, to fall on a screen placed in a horizontal position : by this means the spectators are enabled to see the images in erect positions. [CAMERA LUCEDA AND CAMERA
OBSCURA.] When the construction of the building is such as to allow the ball and lens to be fixed at an aperture in the roof, a plane mirror being placed above it at an angle of 45 degrees with the horizon, so as to reflect the rays from external objects down on the lens, the images formed on a screen within the darkened apartment are more distinctly formed and more conveniently seen. An apparatus of this nature was formerly applied to the roof of a building connected with the astro nomical observatories at Greenwich, Edinburgh, and Glasgow, for the amusement of visitors.