"[...] A section of a sphere, by a plane cutting it in any manner, is a circle. Great circles are those which pass through the centre of the sphere, and divide it into two equal hemispheres. Small circles are such as do not pass through the centre, but divide the sphere into two unequal parts. The axis of a circle is a straight line passing through its centre at right angles to its plane. The pole of a great circle is the point on the sphere where its axis cuts through the sphere. Every great circle has two poles, each of ...
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"[...] A section of a sphere, by a plane cutting it in any manner, is a circle. Great circles are those which pass through the centre of the sphere, and divide it into two equal hemispheres. Small circles are such as do not pass through the centre, but divide the sphere into two unequal parts. The axis of a circle is a straight line passing through its centre at right angles to its plane. The pole of a great circle is the point on the sphere where its axis cuts through the sphere. Every great circle has two poles, each of which is every where ninety degrees from the great circle. All great circles of the sphere cut each other in two points diametrically opposite, and consequently their points of section are one hundred and eighty degrees apart. A great circle, which passes through the pole of another great circle, cuts the latter at right angles. The great circle which passes through the pole of another great circle, and is at right angles to it, is called a secondary to that circle. The angle made by two great circles on the surface of the sphere is measured by an arc of another great circle, of which the angular point is the pole, being the arc of that great circle intercepted between those two circles.[...]."
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