This call'd the Horizon, is the Round's Defign,
For 'tis, to bound, gives Title to the Line.

Aftron. Book I.

Euphrof. The Poet intimates what I was juft going to obferve, viz. that this Circle must always be variable and new, according to the different Situation of the Spectator on the Surface of the Globe, or Sphere.

Cleon. Very true, Euphrofyne; every Perfon has an Horizon peculiar to himself. Thus the People of Paris have a different Horizon from that of the People at London, or Madrid; their vifible Hemifphere extending more to the South than that of the former, and lefs than that of the latter. All which I fhall more fully explain to you on the terrestrial Globe.

Euphrof. But, pray, what is this other Circle on the outer Part of the Horizon, marked all round with Letters? Clean. This Circle is called the Compafs; it is of great Ufe at Sea; and alfo in the Sciences of Aftronomy and Geography; for which Reafon it is fixed on the Horizon of Spheres and Globes.

Euphrof. What are thofe various Divifions in it, by which the Letters ftand?

Cleon. They are called the Points of the Compass;_and are 32 in Number, each cont ining 11 Degrees. Four of which are called the Cardinal Points, and are marked with the first Letter of their Names, viz. S, the South; W, the Weft; N, the North; E, the Eaft. These four principal Points are fometimes called the four Winds of Heaven. They divide the Horizon, you fee, into four Quarters, in each of which are eight Points.

Euphrof. What are the Names of thefe intermediate Points?

Cleon. They receive their Names from their relative Distances from the four Cardinal Points, in each Quarter respectively; which Names are denoted by the initial Letters alfo.

Thus in the Quarter between the South and West, the Points are denominated as follows:

I. S.

2. S. by W.

3. S. S. W.

4. S. W. by S.

SOUTH.

SOUTH by WEST.
SOUTH-SOUTH-WEST.

SOUTH-WEST by SOUTH,

After the fame Manner, you fee, the Points in the other Quarters are named as denoted by the Capital Letters.

Euphrof. I understand you perfectly well, as to that; but what is the Ufe of these Points?

Cleon. By them we ufually distinguish the Course of the Winds and Clouds, and give them their proper Names ; thus if the Wind blows from the North-East Point, we fay it is a North-Eaft Wind; and the Courfe of the Clouds we fay is South-West, which is oppofite to it.

Again, in Geography, we thereby distinguish and relate the Situation and Bearing of Places, Countries, or Cities, one from another: Thus, we fay, Bourdeaux in France lies South of London; and Bagdat bears South-East from London.

Lastly; in Aftronomy, we fay, the Sun, Moon, or Planets, rife on fuch or fuch a Point; or fo many Points from the Eaft or Weft toward the South or North; which Diftance from the Eaft or Weft Point is called the Amplitude of their Rifing or Setting. I fhall not mention the Ufe of the Compafs at Sea, as yet.-Thefe are the chief Uses that it ferves for in common, and are fummarily included in the following Verfes :

The Compafs-Points by Art have been defign'd,
To fhew the various Courfes of the Wind;

From hence the Seaman, hence the Farmer knows,
If North, South-Eaft, or South-South-Weft it blows;
ihence they, or Calms, or Tempefts, oft prefage,
And fhew their Skill in Heav'n's prophetic Page.
Their Ufe in Geography doth hence appear,
They fhew from us how all the Countries bear;
Of Towns from Towns the varied Site we learn,
And Trav❜lers hence the dubious Way difcern.
From hence, in Aftronomic Phrafe, we say,
On fuch a Point Sol ufhers in the Day;
Or fets Alderbaran; or Cynthia bright,
Drive Weft by South the Chariot of the Night.

Euphrof. Well, I never knew fo much of the Compass, and its Ufe, before; but I fee now it is very confiderable: If there remain any other Ufes of the Horizon, or Compass, which we have not enquired into, pray, let me know them, Cleonicus.

Cleon. What remains will be better explained when we come to the Globes; at prefent we will proceed to the General Meridian, and confider its Properties.

DIALOGUE

III.

Of the GENERAL MERIDIAN, and the Degrees of

I

Latitude.

Euphrofyne.

Obferve the Names of thefe Circles import fomething of their Nature and Ufe; pray, what is implied by the Name of this Circle, the Meridian?

Cleon. It is derived of the Latin Word Meridies, which fignifies Mid-day, or Noon; because, when the Sun comes upon the Meridian of any Place, it is then Noon, or Mid-day, at that Place.

Euphrof. Very good; but why do you call it the General Meridian?

Cleon. To diftinguish it from particular Meridians : Now you must know, that a particular, or special Meridian, is an imaginary Circle in the Heavens, which passes through the Poles of the World, and the Zenith Point of every Perfon wherefoever fituated on the Earth's Surface: Confequently, there will be as many fuch Meridians as you can imagine Points from Eaft to Weft, all round the Earth; for those which lie North and South of each other, have the fame Meridian; because thefe Circles lie North and South themfelves. Now, in Spheres and Globes, this general Meridian fuffices for all the reft; for fince it is fixed, and the Sphere or Globe is moveable about its Axis under it, you may by turning the fame, bring any different Part of their Surface under this Meridian, which will then represent the Meridian of that Part or Place.

Euphrof. So the Office of this Meridian, I perceive, is vicarious, viz. to reprefent all, or any of the reft. Well, fince you have let me into the Reafon and Significancy of the Nature or Title, let me next know what these Divifions or Degrees are upon it, and to what Use they ferve.

Cleon. I will: You obferve they begin at the Equinoctial, and proceed each Way to the North and South Pole of the World, to the Number of 90.

Euphrof. I do; and pray what do you call them?

Cleon. They are called the Degrees of Latitude on the Terreftrial Globe: By the Word Latitude you are to understand any Diftance, North or South of the Equinoctial, towards the Poles; and because fuch a Distance of any Place on the Globe, is estimated by these Degrees, you will readily fee the Reason of their Name.

Euphrof. I do very plainly; but why are thofe Degrees numbered a contrary Way on the other Half of the Meridian, or that under the Horizon? for they are reckoned from the Poles towards the Equinoctial there, I fee.

Cleon. That's well obferved, Euphrofyne; the Divifions are there numbered a contrary Way, the Defign of which is, that the Height, or Elevation of the Pole above the Horizon may be readily feen, in any Pofition of the Sphere; and this Elevation of the Pole is always equal to the Latitude of any Place on the Earth's Surface.

Euphrof. I prefume you mean, that fo many Degrees as any Place lies North or South from the Equinoctial, juft fo many Degrees will the North or South Pole appear above the Horizon of that Place. But how fhall I be able to conceive the Truth of this?

Clean. Very eafily, if you confider, that from the Equinoctial (Q) to the Pole (N) are just 90 Degrees; alfo from the given Place (Z) to the Horizon (R) are juft go Degrees; but the Part between the Place and the Pole, (ZN) is included in both those Quadrants; and therefore, if it be fubducted from both, the Remainders will be equal; that is, the Arch (QZ) will be equal to the Arch (NR), or the Latitude (QZ) of the Place (Z) is equal to the Height, or Elevation (NR) of the Pole (N).

Euphrof. I believe I apprehend the Meaning; but, pray, Cleonicus, what would you infer from thence?

Cleon. A very important Úfe is made of this in divers practical Arts: Thus the Geographer ard Diallift, by taking the Height of the Pole Star with a good Quadrant, know the Latitude of the Place; by this Means also, the Sailor finds his Latitude at Sea, hence likewise we have a fpeedy Method of rectifying a Sphere, or Globe, as we thall farther fee by and by.

Euphrof. What farther Ufes are made of this great Circle?

Cleon. By Means thereof, we also measure the Diftances of the Sun, Planets, or Stars from the Equinoctial, North or South; and the Degrees, or Distance of this Sort, are called the Declination of thofe Bodies from the Equinoctial.Thus fuppofe the higheft or most Northern Part of the Ecliptic be brought to the Meridian, you fee it cut the fame in 23 Degrees; and fo much is the Declination of that Point :-Which you fee is the fame alfo on the South Side. The Declination alfo of the Polar Circle you obferve is 66 on each Side the Equinoctial.

Euphrof. I do fo; and have now gotten a pretty good Notion of Latitude and Declination. But, pray, what is the Use of this thin, long Slip of Brafs, which I saw you at firft take off from the Meridian?

Cleon. It is called the Quadrant of Altitude; because it is just a Quarter of a Circle, and divided into 90 Degrees; and being fixed on the higheft, or vertical Point of the Meridian (Z) reaches to the Horizon all around; and being moveable on a Pin at the Meridian, it may be carried to any Part on the Sphere or Globe; and fo will fhew the Height or Altitude of the Sun, or any Star above the Horizon, at any Time, or in any Pofition of the Sphere. Alfo being laid over any Place, it fhews how that Place bears from you by the Points of the Compafs on the Horizon. Alfo, by this you will be taught how to Measure, in Degrees, the Distance of any two Places on the Terreftrial Globe, or of any two Stars in the celeftial. The graduated Edge of this Quadrant reprefents on the Globe thofe imaginary Circles, which the Aftronomers call Azimuths, or Circles of Altitude, and

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