powder of projection

Projection \Pro*jec"tion\, n. [L. projectio: cf. F. projection.]
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   1. The act of throwing or shooting forward.
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   2. A jutting out; also, a part jutting out, as of a building;
      an extension beyond something else.
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   3. The act of scheming or planning; also, that which is
      planned; contrivance; design; plan. --Davenant.
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   4. (Persp.) The representation of something; delineation;
      plan; especially, the representation of any object on a
      perspective plane, or such a delineation as would result
      were the chief points of the object thrown forward upon
      the plane, each in the direction of a line drawn through
      it from a given point of sight, or central point; as, the
      projection of a sphere. The several kinds of projection
      differ according to the assumed point of sight and plane
      of projection in each.
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   5. (Geog.) Any method of representing the surface of the
      earth upon a plane.
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   {Conical projection}, a mode of representing the sphere, the
      spherical surface being projected upon the surface of a
      cone tangent to the sphere, the point of sight being at
      the center of the sphere.

   {Cylindric projection}, a mode of representing the sphere,
      the spherical surface being projected upon the surface of
      a cylinder touching the sphere, the point of sight being
      at the center of the sphere.

   {Globular}, {Gnomonic}, {Orthographic}, {projection},etc. See
      under {Globular}, {Gnomonic}, etc.

   {Mercator's projection}, a mode of representing the sphere in
      which the meridians are drawn parallel to each other, and
      the parallels of latitude are straight lines whose
      distance from each other increases with their distance
      from the equator, so that at all places the degrees of
      latitude and longitude have to each other the same ratio
      as on the sphere itself.

   {Oblique projection}, a projection made by parallel lines
      drawn from every point of a figure and meeting the plane
      of projection obliquely.

   {Polar projection}, a projection of the sphere in which the
      point of sight is at the center, and the plane of
      projection passes through one of the polar circles.

   {Powder of projection} (Alchemy.), a certain powder cast into
      a crucible or other vessel containing prepared metal or
      other matter which is to be thereby transmuted into gold.
      

   {Projection of a point on a plane} (Descriptive Geom.), the
      foot of a perpendicular to the plane drawn through the
      point.

   {Projection of a straight line of a plane}, the straight line
      of the plane connecting the feet of the perpendiculars let
      fall from the extremities of the given line.
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   Syn: See {Protuberance}.
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