198. If the reader be hitherto unacquainted with the principal circles of the Globe, he should now learn to know them; which he may do sufficiently for his present purpose in a quarter of an hour, if he sets the ball of a terrestrial Globe before him, or looks at the Figure of it, wherein these circles are drawn and named. The _Equator_ is that great circle which divides the northern half of the Earth from the southern. The _Tropics_ are lesser circles parallel to the Equator, and each of them is 23-1/2 degrees from it; a degree in this sense being the 360th part of any great circle which divides the Earth into two equal parts. The _Tropic of Cancer_ lies on the north side of the Equator, and the _Tropic of Capricorn_ on the south. The _Arctic Circle_ has the _North Pole_ for it’s center, and is just as far from the north Pole as the Tropics are from the Equator: and the _Antarctic Circle_ (hid by the supposed convexity of the Figure) is just as far from the _South Pole_, every way round it. These Poles are the very north and south points of the Globe: and all other places are denominated _northward_ or _southward_ according to the side of the Equator they lie on, and the Pole to which they are nearest. The Earth’s _Axis_ is a straight line passing through the center of the Earth, perpendicular to the Equator, and terminating in the Poles at it’s surface. This, in the real Earth and Planets is only an imaginary line; but in artificial Globes or Planets it is a wire by which they are supported, and turned round in _Orreries_, or such like machines, by wheel-work. The circles 12. 1. 2. 3. 4, _&c._ are Meridians to all places they pass through; and we must suppose thousands more to be drawn, because every place that is ever so little to the east or west of any other place, has a different Meridian from that other place. All the Meridians meet in the Poles; and whenever the Sun’s center is passing over any Meridian, in his apparent motion round the Earth, it is mid-day or noon to all places on that Meridian. [Sidenote: Zones.] 199. The _broad Space_ lying between the Tropics, like a girdle surrounding the Globe, is called the _torrid Zone_, of which the Equator is in the middle, all around. The _Space_ between the Tropic of Cancer and Arctic Circle is called the _North temperate Zone_. _That_ between the Tropic of Capricorn and the Antarctic Circle, the _South temperate Zone_. And the two _circular Spaces_ bounded by the Polar Circles are the two _Frigid Zones_; denominated _north_ or _south_, from that Pole which is in the center of the one or the other of them. 200. Having acquired this easy branch of knowledge, the learner may proceed to make the following experiment with his terrestrial ball; which will give him a plain idea of the diurnal and annual motions of the Earth, together with the different lengths of days and nights, and all the beautiful variety of seasons, depending on those motions. [Sidenote: Fig. III.