125. The Earth’s bulk is but a point, as that at _C_, compared to the Heavens; and therefore every inhabitant upon it, let him be where he will, as at _n_, _e_, _m_, _s_, &c. sees one half of the Heavens. The inhabitant _n_, on the North Pole of the Earth, constantly sees the Hemisphere _ENQ_; and having the North Pole _N_ of the Heavens just over his head, his [25]Horizon coincides with the Celestial Equator _ECQ_. Therefore all the Stars in the Northern Hemisphere _ENC_, between the Equator and North Pole, appear to turn round the line _NC_, moving parallel to the Horizon. The Equatoreal Stars keep in the Horizon, and all those in the Southern Hemisphere _ESQ_ are invisible. The like Phenomena are seen by the observer _s_ on the South Pole, with respect to the Hemisphere _ESQ_; and to him the opposite Hemisphere is always invisible. Hence, under either Pole, only one half of the Heavens is seen; for those parts which are once visible never set, and those which are once invisible never rise. But the Ecliptic _YCX_ or Orbit which the Sun appears to describe once a year by the Earth’s annual motion, has the half _YC_ constantly above the Horizon _ECQ_ of the North Pole _n_; and the other half _CX_ always below it. Therefore whilst the Sun describes the northern half _YC_ of the Ecliptic he neither sets to the North Pole nor rises to the South; and whilst he describes the southern half _CX_ he neither sets to the South Pole nor rises to the North. The same things are true with respect to the Moon; only with this difference, that as the Sun describes the Ecliptic but once a year, he is for half that time visible to each Pole in it’s turn, and as long invisible; but as the Moon goes round the Ecliptic in 27 days 8 hours, she is only visible for 13 days 16 hours, and as long invisible to each Pole by turns. All the Planets likewise rise and set to the Poles, because their Orbits are cut obliquely in halves by the Horizon of the Poles. When the Sun (in his apparent way from _X_) arrives at _C_, which is on the 20th of _March_, he is just rising to an observer at _n_ on the North Pole, and setting to another at _s_ on the South Pole. From _C_ he rises higher and higher in every apparent Diurnal revolution ’till he comes to the highest point of the Ecliptic _y_, on the 21st of _June_, and then he is at his greatest Altitude, which is 23-1/2 degrees, or the Arc _Ey_, equal to his greatest North declination; and from thence he seems to descend gradually in every apparent Circumvolution, ’till he sets at _C_ on the 23d of _September_; and then he goes to exhibit the like Appearances at the South Pole for the other half of the year. Hence the Sun’s apparent motion round the Earth is not in parallel Circles, but in Spirals; such as might be represented by a thread wound round a Globe from Tropic to Tropic; the Spirals being at some distance from one another about the Equator, but gradually nearer to each other as they approach nearer to the Tropics.