A compendium of astronomy; containing the elements of the science, familiarly explained and illustrated, with the latest discoveriesAdapted to the use of schools and academies, and of the general reader . se; and as we continue toturn it more and more round, the ellipse grows narrowerand narrower, until, when the edge is presented to theeye, we see nothing but a line. Now imagine the ringto be near a perpendicular wall, and the eye to be re- 30. What is particularly recommended to the young learner ? 31 What is meant by the projection of the sphere 1 Whatis the projection of a circle when seen
A compendium of astronomy; containing the elements of the science, familiarly explained and illustrated, with the latest discoveriesAdapted to the use of schools and academies, and of the general reader . se; and as we continue toturn it more and more round, the ellipse grows narrowerand narrower, until, when the edge is presented to theeye, we see nothing but a line. Now imagine the ringto be near a perpendicular wall, and the eye to be re- 30. What is particularly recommended to the young learner ? 31 What is meant by the projection of the sphere 1 Whatis the projection of a circle when seen directly before the face ?what when seen obliquely 1 what when seen edgewise 1 20 THE EARTH. moved at such a distance from it, as not to distinguishany interval between the ring and the wall; then theseveral figures under which the ring is seen, will appearto be inscribed on the wall, and we shall see the ring asa circle when perpendicular to a straight line joiningthe center of the ring and the eye, as an ellipse whenoblique to this line, or as a straight line when its edge istowards us. 32. It is in this manner that the circles of the sphereare projected, as represented in the following diagram. Here various circles are represented as projected on themeridian, which is supposed to be situated directly be-fore the eye, at some distance from it) .The horizon HObeing perpendicular to the meridian is seen edgewise, andconsequently is projected into a straight line. The sameis the case with the prime vertical ZN, with the equatorEQ, and the several small circles parallel to the equator,which represent the two tropics and the two polar cir- 32. In figure 5, what represents the plane of projection ?Why are certain circles represented by straight lines 1 why areothers represented by ellipses ? How is the eye supposed tobe situated ? DIURNAL REVOLUTION. 21 cles. In fact, all circles whatsoever, which are perpen-dicular to the plane of projection, will be representedby straight lines.
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Keywords: ., bookcentury1800, bookdecade1850, booksubjectastronomy, bookyear18
