Camera Obscura

an optical instrument used to view or sketch objects at a short distance. It consists of a box, formed of two parts sliding in each other, like a telescope, so as to adjust the focus to bodies more or le distant. A tube with a lens is fixed in one side of it, and is turned to the object to be represented. The rays entering fall on a mirror sloped at an angle of 45°, which reflect them. upward. It is convenient that they may be made to pa through a horizontal plate of gla , on which tracing paper may be placed so as to enable one to draw the figure.