POINCON, Fr. A puncheon, bodkin. It is likewise an instrument which is used in the making of artificial fireworks, being called poincon à arrêt, from a piece of iron running cross-ways near the point, to prevent it from entering too far.
POINT, in geometry, according to Euclid, is a quantity which has no parts, being indivisible; and according to others, that which terminates itself on every side, or which has no boundaries distinct from itself. This is a mathematical point, and is only conceived by the imagination; yet herein all magnitude begins and ends, its flux generating a line, that of a line a surface, &c. A line can only cut another in a point.
Point, in perspective, denotes various places with regard to the perspective plane, viz. point of sight, or of the eye, or principal point, is a point in the axis of the eye, or in the central ray, where the same is intersected by the horizon.
Point, or points of distance, in perspective, is a point or points, for there are sometimes two of them placed at equal distances from the point of sight.
Accidental POINTS, or Contingent POINTS, in perspective, are certain points wherein such objects as may be thrown negligently, and without order, under the plan, do tend to terminate. For this reason they are not drawn to the point of sight, nor the points of distance, but meet accidentally, or at random in the horizon.
Point of the front, in perspective, is when we have the object directly before us, and not more on one side than the other, in which case it only shews the foreside; and if it be below the horizon, a little of the top too, but nothing of the side, unless the object be polygonous.
Third POINT, is a point taken at discretion in the line of distance, wherein all the diagonals drawn from the divisions of the geometrical plane concur.
Objective POINT, a point on a geometrical plane, whose representation is required on the perspective plane.
Point of concourse, in optics, is that wherein converging rays meet, more commonly called the focus.
Point of dispersion, is that wherein the rays begin to diverge, usually called the virtual focus.