The English globe being a stabil and immobil one, performing what the ordinary globes do, and much more / invented and described by the Right Honorable, the Earl of Castlemaine ; and now publish't by Joseph Moxon ...

Operation II. To find the Suns Almucantar, or Height.

THere are three distinct ways of performing this indepen∣dent of the following Operations, and each of great use; for the first gives you the Suns height in an instant if he shines. The second if you have the least glimps of him, or can guess at his place in a Cloud. The third, if you know the hour by any good Watch, Pendulum or the like, whether we see the Heavens or no.

I. As for the first way, 'tis this; your Globe being level,* 1.1 move it 'till the shade of the Pin in the Zenith falls directly upon

the Meridian, and then the shade of the Extuberancy (i. e. that made by the swelling or bellying out of the Globe) will touch the true degree in the Quadrant of Altitude reckoning from the Ze∣nith to it. And thus you will find not only the Sun's height, sooner perchance than by any ordinary Quadrant, but will still have it before your eyes as long as you please, nothing being to be fur∣ther done, but to move sometimes the Globe that the shade of the said Pin may still concur with the Meridian. But if your Globe be fix'd, (or that for some particular reason, you have no mind to stir it at all, draw your string from the Zenith, through the shade of its Pin, i. e. lay the string in the Plane of the Sun, and then if you mount your Bead till it reaches the nearest part of the shade of Extuberancy, it will (by bring∣ing it to the Meridian or Quadrant of Altitude) lye on the true Degree, reckoning (as before) from the Zenith to it.

The Reason of the Operation is this; The Sun when he rises* 1.2 brushes the Zenith and Nadir of the Globe with his Rayes, for he illuminates alwayes (within some few Minutes) just half of it, therefore when he gets (v. g.) a Degree higher, he must needs illuminate a Degree beyond the Zenith, and so proporti∣onably from time to time, or else he would sensibly illuminate more or less of the Globe at one moment than at another, which* 1.3 is absurd. Now since the Sun in truth illuminates more than an Hemispere, the Reader must remember that Ptolomy rec∣kons this excess (take one time with another) to be about 26 minutes, and Tycho something less, therefore substract 13 mi∣nutes (or half the said Excess) from what the shade of Extube∣rancy mark's, and you have his Height with all ordinary Exact∣ness: but should you chance at any time to doubt how far the said Shade of Extuberancy (which is not so discernable as that* 1.4 made by a Gnomon) just reaches, erect then a piece of stick, straw, quill, &c. or, if you please, rest your Finger on the Globe, between the Sun and the point in dispute, and where the shade of your Finger, straw, stick or quill is lost, that will be the true Term of the shade.

As for the Second Way (for both the former we reckon but* 1.5 one) turn the Meridian of your Globe to the Sun as before, or because we suppose him not to shine out-right, direct by your Eye the said Meridian, so that it lye in the same Plain with him, and this you may do in a manner as well (if you have the

least glimps of him, or can by any accident guess whereabouts he is) as if you had the fore-mentioned help of the Pin's shade in the Zenith. Having thus done, Take your String in both hands, and cross with it (as exactly as you can at right Angles) that part of the Meridian next your body, whether it happens to be the Quad. of Alt. or that of Proportion, then putting your Face close to it, and moving your Ey lower and low∣er, till by reason of the Extuberancy you can but just see the Sun, or his supposed place in Heaven, do but bring your String (held as before) to this point, viz. bring your String towards you till it just takes away the Sun or his supposed place from your Ey, and the degree in the Meridian on which it then lies will be (counting from the Zenith) the Height re∣quired; for so far his raies would reach did he shine out-right.

The third way is when we know the Hour by any Watch, Pendulum,* 1.6 &c. thus, Find among the Aequin. or Diurnal Parallels that belonging to the present Day, which we will suppose Apr. 10. and drawing your string from the Zenith over that Point in the said Parallel, where 'tis cut by the Hour given, i. e. by the morning 9 a Clock Circle, move your Bead to the said Point, and the distance from the Bead to the Horizon will be the required Height, viz. about 36 degrees, as you'l find if you bring the Bead to the Meridian and count the degrees between it and the Horizon.

The Suns Height may be also known by its Azimuth, as by Operat. 5.* 1.7 Having therefore by any of the aforesaid waies his Height, 'twill (upon any doubt) soon appear whether it be Fore or Afternoon, for as long as ever he increases in Degrees, i. e. mounts higher and higher above the Ho∣rizon, it wants of Noon, whereas if he falls or declines, 'tis after Noon.

Notes

• * 1.1

  The first way.
• * 1.2

  The Reason and Domon∣stration of the operation.
• * 1.3

  How much the Sun illu∣minates more than half the Earth.
• * 1.4

  How to know the terms of the shade of Extuberancy when the sun shines faintly.
• * 1.5

  The second Way.
• * 1.6

  The Third way.
• * 1.7

  To know at any time whether it be Forenoon or After∣noon.