230 GEOGRAPHY AND ASTRONOMY. cal motion'', and advances 50 seconds or almóst a minute of a degree every year, which amounts to one whole degree in 72 years, and will fulfil a complete revolution in 25,920 years. This period some have called the platonical year, when some of the ancients fancied all things should return into the same state in which they now are. Yet we call these equinoctial and solsticial points in the heaven, and all the parts of the ecliptic by the same ancient names still in astronomy, and mark them still with the same characters viz. i', tj, fi, 2D, 9,, &c. though the constella- tions themselves seem to be removed so much forward. XIII, andXIV. Here it may not be improper in the last place to mention the poles of the ecliptic which are two other points marked generally in the celestial globe. If there were an axis thrust though the centre of the globe just at right angles with the plane of the ecliptic, its ends or poles would be found in the two polar circles. So that a quarter of a circle or 90 degrees numbered directly or perpen- dicularly from the ecliptic line spew the poles of the ecliptic, and fix these two points through which the two polar circles are drawn. It is usual also in books of this kind to mention two great circles called colures, drawn sometimes on the celestial globe through the poles` of the world, one of which cutting the ecliptic in the two solsticial points is called the solsticial colore ; the other cutting it in the equinoctial points is called the equinoctial colore, but they are not of much use for anycommon purposes or ,practices that relate to the globe. I think it may not be amiss before we proceed farther, to let the learner see a representation of all the foregoing circles and points on the globe, just as they stand in our horizon at Lon- don, and so far as they can be represented on a flat surface, and in strait lines. Let the northpole be raised above the north part of fhe hori- zon 511 degrees which are numbered on the brazen meridian, then let the globe be placed at such a distance as to make the convexity insensible, and appear as a flat or plain surface, and let the eye of the spectator be just level and opposite to which represents the east point of the horizon: then the globe and the circleson it will appear nearly asrepresented in Figure tit. The large circle divided by every5 degrees represents the meridian, the rest of the larger and the lesser circles are there a: The axis pf the earth is supposed to be fastened at its middle in the centre, while both ends of it, or each of the roles in th:a motion describes a circle coned each pole of the ecliptic, which is the hase of the cone. The vertexes of each of these cones meet in t'e centre of the earth ; and by this motion of the earth, all the fixt stars seem to be mored from their former places in circles parallel to the ecóptic.
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