This Figure represents a Globe, whereon are drawn the Meridians or Hour-Circles. There are divers Sizes of them; the great ones are set up in Gardens, and are of Stone or Wood well painted, and the small ones are made of Brass, having Compasses belonging to them, and may be reckoned among the Number of Portable Dials.
The manner of turning round Balls of any Matter is well known, but if a large Stone-Ball is to be made, that cannot be turned because of it’s Weight: first, you must nighly form it with a Chissel, and then take a wooden or brass Semi-Circle of the same Diameter as you design your Ball. This being done, turn the Semi-Circle about the Ball, and take away all the Superfluities with a Raspe, until the Semi-Circle every where and way just touches the Superficies thereof; afterwards make it smooth with a Pumice-Stone or Sea-Dog Fish’s Skin, &c.
The Globe being well rounded and made smooth, you must take the Diameter thereof with a Pair of Spheric Compasses, viz. such whose Points are crooked, which suppose the right Line AB; this Line is divided into two equal Parts in E by the vertical Line ZN, the upper Point whereof Z, represents the Zenith, and the lower one N, the Nadir. Now set one Point of the Spheric Compasses in E, and extend the other to A, and draw the Meridian Circle AZBN; likewise setting one Foot of your Compasses in Z, with the last Opening describe the Circle AEB, representing the Horizon; and from the Point B to C count 49 Deg. the Elevation of the Pole on the Meridian, and setting one Foot of your Compasses in the Point C, representing the North Pole, extend the other to 41 Deg. on the Meridian below the Point B, and draw the Equinoctial Circle; likewise setting one Foot of your Compasses, opened to the same Distance as before, upon the Point in the Meridian cut by the Equinoctial, you may draw the Hour-Circle of 6 passing thro’ the Poles C and D. By this means the Equinoctial shall be divided into four equal Parts by the Meridian and Hour-Circle of 6; and if each of these four Parts be divided into six equal Parts, for the 24 Hours of a Natural Day, and about the Points of Division as Centers, with the extent of a Quadrant of the Globe, Circles be described; these will all pass thro’ the Poles of the World C and D, and are the Hour-Circles. If you have a mind to have the half Hours or Quarters, each of the Divisions on the Equinoctial must be divided into 2 or 4 equal Parts. The Hour-Circles are numbered round the Equinoctial both above and below it, as appears per Figure.
If the Parallels of the Signs are to be drawn upon the Globe, you must count Upon the Meridian both ways from the Equinoctial, the Declination for every Sign, according to the Table expressed; as, for Example, For the two Tropicks you must count 23 Deg. 30 Min. from the Equinoctial, and about the Poles C and D, draw Circles on the Globe. Note, The two Polar Circles must be drawn at 23 Deg. 30 Min. from the Poles, or 66 Deg. 30 Min. from the Equinoctial.
The Globe thus ordered must be placed upon a Pedestal proportionable to the bigness thereof in a Hole made in the Nadir N, distant from the Pole the Complement of it’s Elevation (viz. 41 Deg.) and fixed in a Garden, or elsewhere, well exposed to the Sun, so as to be conformable to the Sphere of the World.
But if it be a small Portable Globe, we place a little Compass upon the Pedestal thereof, that so the Globe may be set North and South when the Hour of the Day is to be shewn thereby, which is shewn thereon without a Style, by the Shadow of the same Globe: for the Shadow or Light thereon always occupies one half of the Globe’s Convexity, when the Sun shines upon it; and so the Extremity of the Shadow or Light shews the Hour in two opposite Places. If, moreover, the different Countries on the Earth’s Supersicies, as likewise the principal Cities, are laid down upon the Globe according to their true Latitudes and Longitudes, you may discover any Moment the Sun shines upon the same, by the illuminated part thereof, what Places of the Earth the Sun mines upon, and what Places are in Darkness. The Extremity of the Shadow shews likewise what Places the Sun is rising or setting at; and what Places have long Days, and what have short Nights: you may likewise distinguish thereon the Places towards the Poles that have perpetual Night and Day. All this is easy to be understood by those who are acquainted with the Nature of the Sphere. Note, This Dial is the most natural of all others, because it resembles the Earth itself, and the Sun mines thereon as he does on the Earth.
You may find the Hour of the Day otherwise, by means of a thin brass Semi-Circle divided into twice 90 Deg. adjusted to the Poles or Extremes of the Axis, by help of two little Ferrils. This Semi-Circle being turned about the Globe with your Hand, until it only makes a perpendicular Shadow upon the Globe, represents the Hour-Circle wherein the Sun is, and consequently shews the Hour of the Day, and also what Places of the Earth it is Noon at that Time. But in this Case the Number 12 must be set to the Meridian, and the Numbers 6 and 6 to the two Points wherein the Equinoctial cuts the Horizon: and this is the reason why we commonly place two rows of Figures along the Equinoctial. The Shadow of the two ends of the Axis, if they are continued out far enough beyond the Poles, and the Hours are figured round the Polar Circles, will likewise shew the Hour. Note, In order to make small Portable Globes universal, we adjust Quadrants underneath them, that so the Pedestal may be slid according to the Elevation of the Pole. This is easy to be understood.