Ouranoskopia, or, The contemplation of the heavens, in a perpetual speculum, or general prognostication for ever wherein is succinctly demonstrated the names and natures of the signs, planets and aspects, terms of art, order of the spheres, the colours, magnitudes, motions, solid proportions and distances of the seven planets from the earth ... / by Iames Corss ...

CHAP. XXVI. Of the description of the Quadrant, and how to find the Altitude of the Sun, Moon or Stars thereby.

FIrst, having prepared a peece of Box-wood, Pear-tree, Walnut-tree, or good Plain-tree, well plain'd and smooth'd on both sides, in manner of a Quadrant. Draw thereon the two Semidiamiters, A B, and A C, in such manner as they may cut one another, at right Angles (or Square-wayes) in the Center A. Upon which Center A, set on foot of your Compasses. And

[illustration] diagram of a quadrant

(opening the other to as much a convenient distance as you think fit) with the other describe the Arch, B C. This Arch is called the Limb of the Quadrant, and is di∣vided into 90 equal parts, called degrees thus. First, divide the Arch, B C, into three parts, then every third into three again, so have you nine. Now if ye divide every of those nine into two, so you have 18 parts.

Lastly, If you divide each of these 18 into 5, the total will be 90 degrees. Which (you may sub-divide if quan∣tity will give live) numbred from the left hand towards the right, marking it with 10, 20, 30, 40, &c. unto 90 after the usual manner.

As for the Square within, ye shall draw from either side of your Quadrant a right Line, cutting one another at right Angles at the midle of the Quadrant, which is 45 degrees. This Scale or Square you may divide into 12, 60, 100, or 1000, (the more the better and more commodious) equal parts, all marked from the Center A. That side of the Square next the sights, is called, Ʋmbra recta, or parts of right shaddow. The other side is called, Ʋmbra versa, or points of contrary shaddow.

To this Quadrant (as to all others of this kind in their use) you must place two sights upon the Line A C, with a Line and Plummet, hanging up in the Center A, and so your Quadrant is finished.

Now to find the Altitude of the Sun, Moon or Stars thereby.

HOld up your Quadrant to the Sun (the Threed and Plummet having their free course hanging in the Center A,) moving it up or down, untill you see that both the sights have received the Sun Beams: At which instant mark the fall of the Line and Plummet, for it will cut (upon the Limb of your Quadrant) the degree and minut of the Suns Altitude, at the time of your obser∣vation.

But if you desire (in the night time) to find the

Altitude of the Planets or fixed Stars, then set the Qua∣drant to your eye, looking through both the sights, un∣till you espy that Planet or Star whose Altitude you re∣quire, which having found, your Plummer hanging at liberty, mark the fall thereof upon the Quadrants Limb, and it will show you the Altitude of that Coelestial Bo∣dy, as you required.