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Polar projection
(gcide) | Polar \Po"lar\, a. [Cf. F. polaire. See Pole of the earth.]
1. Of or pertaining to one of the poles of the earth, or of a
sphere; situated near, or proceeding from, one of the
poles; as, polar regions; polar seas; polar winds.
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2. Of or pertaining to the magnetic pole, or to the point to
which the magnetic needle is directed.
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3. (Geom.) Pertaining to, reckoned from, or having a common
radiating point; as, polar coordinates.
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Polar axis, that axis of an astronomical instrument, as an
equatorial, which is parallel to the earths axis.
Polar bear (Zool.), a large bear (Ursus maritimus syn.
Thalarctos maritimus) inhabiting the arctic regions. It
sometimes measures nearly nine feet in length and weighs
1,600 pounds. It is partially amphibious, very powerful,
and the most carnivorous of all the bears. The fur is
white, tinged with yellow. Called also White bear. See
Bear.
Polar body, Polar cell, or Polar globule (Biol.), a
minute cell which separates by karyokinesis from the ovum
during its maturation. In the maturation of ordinary ova
two polar bodies are formed, but in parthogenetic ova only
one. The first polar body formed is usually larger than
the second one, and often divides into two after its
separation from the ovum. Each of the polar bodies removes
maternal chromatin from the ovum to make room for the
chromatin of the fertilizing spermatozoon; but their
functions are not fully understood.
Polar circles (Astron. & Geog.), two circles, each at a
distance from a pole of the earth equal to the obliquity
of the ecliptic, or about 23[deg] 28', the northern called
the arctic circle, and the southern the antarctic circle.
Polar clock, a tube, containing a polarizing apparatus,
turning on an axis parallel to that of the earth, and
indicating the hour of the day on an hour circle, by being
turned toward the plane of maximum polarization of the
light of the sky, which is always 90[deg] from the sun.
Polar coordinates. See under 3d Coordinate.
Polar dial, a dial whose plane is parallel to a great
circle passing through the poles of the earth. --Math.
Dict.
Polar distance, the angular distance of any point on a
sphere from one of its poles, particularly of a heavenly
body from the north pole of the heavens.
Polar equation of a line or Polar equation of a surface,
an equation which expresses the relation between the polar
coordinates of every point of the line or surface.
Polar forces (Physics), forces that are developed and act
in pairs, with opposite tendencies or properties in the
two elements, as magnetism, electricity, etc.
Polar hare (Zool.), a large hare of Arctic America ({Lepus
arcticus}), which turns pure white in winter. It is
probably a variety of the common European hare ({Lepus
timidus}).
Polar lights, the aurora borealis or australis.
Polar opposition, or Polaric opposition or {Polar
contrast} or Polaric contrast (Logic), an opposition or
contrast made by the existence of two opposite conceptions
which are the extremes in a species, as white and black in
colors; hence, as great an opposition or contrast as
possible.
Polar projection. See under Projection.
Polar spherical triangle (Spherics), a spherical triangle
whose three angular points are poles of the sides of a
given triangle. See 4th Pole, 2.
Polar whale (Zool.), the right whale, or bowhead. See
Whale.
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Polar projection
(gcide) | 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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