PROJECTION, in perspective, denotes the appearance, or representation of an object on the perspective plane.

The projection, e.g., of a point, as B (Fig. 1, Plate CCCLXXXIII.) is a point b, through which the optic ray BE passes from the objective point through the plane to the eye; or it is the point wherein the plane cuts the optic ray.

And hence is easily conceived what is meant by the projection of a line, a plane, or a solid.

PROJECTION in Alchemy, the casting of a certain imaginary powder, called powder of projection, into a crucible, or other vessel, full of some prepared metal, or other matter; which is to be hereby presently transmuted into gold.

Powder of Projection, or of the philosophers stone, is a powder supposed to have the virtue of changing any quantity of an imperfect metal, as copper or lead, into a more perfect one, as silver or gold, by the admixture of a little quantity thereof.

The mark to which alchemists direct all their endeavours, is to find the powder of projection; which every one of them has been within an ace of a hundred times. See Philosopher's Stone.