The Meridians are commonly drawn upon the Terrestrial Globe thro’ every 15 degrees of the equinoctial, thereby making an Hour difference betwixt the places through which they pass. On the Celestial Globe there are commonly drawn but two of these Meridians, crossing the equinoctial in four points equidistant from one another, thereby dividing it into four quadrants; but the intermediate ones are here supplied, and also upon the Terrestrial Globe, by the brass circle on which they are hung, which, is therefore called the Brass Meridian, and sometimes only the Meridian, it serving for this purpose to all the points upon either Globe.
The Hour Circle.
There is also a little brass circle fixed upon this meridian, divided into 24 Hours, having an index moveable round the axis of the globe, to be turned to any particular Hour. The use of this circle is to shew the difference of time betwixt any two meridians, and is therefore called the Hour Circle.
Parallels of Declination.
3. All circles parallel to the equinoctial are, with respect to any point in the Heavens, called Parallels of Declination. So that,
Declination North and South.
4. The Declination of any Point in the Heavens (as of the Sun, a fixed Star, or the like) is an arch of the meridian passing through that point, and intercepted betwixt it and the equator; and if the said point be to the (Northward/Southward) of the equator, it is called (North/South) Declination.
Tropics and Polar Circles.
Of the parallels of declination, four are eminently distinguished by particular names, viz. The two Tropics, and the two Polar Circles.
Tropic of Cancer; of Capricorn.