when the Sun is in either of them, the Day and Night is every where equal.

4. The firft Points of Cancer and Capricorn are called the Solftical Points * ; because when the Sun arrives at either of them, he seems to ftand in a manner still, in respect to his apparent motion from and towards the Equinoctial, for feveral Days. When he is in one Solftical Point, he makes the longeft Day; when in the other, the shortest, to one and the fame Northern, or Southern Hemisphere.

5% The Point in the Heavens juft over our Head is called the Zenith; and the oppofite Point to it, juft under our Feet, is called the Nadir. These two are the Poles of the Horizon.

Imaginary Circles, drawn thro' the Zenith and Nadir, and cutting the Horizon at right Angles, are called Vertical, or Azimuth Circles. Hence the Distance of the Sun, or a Star, from the Meridian, or South Point of the Heavens, measured by Degrees upon the Horizon, is called its Azimuth; or fometimes the Azimuth is reckoned from any other of the cardinal Points.

The Azimuth of the Sun, or a Star, from due Eaft or Weft, at the Time of its Rifing or Setting, is called its Amplitude.

Solfical, from Solis ftatio, the Sun's Station, or Randing Place.

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6. The

6. The Brass Quadrant of Altitude, fcrewed upon the Zenith, and laid down to the Horizon, represents a Quarter of a vertical Circle. It is called the Quadrant of Altitude, from its Ufe in taking the Altitude, or Height, of the Sun or Stars, above the Horizon, by means of the 90 Degrees marked upon it. The Sun's Height at Noon above the Horizon is called his Meridian Altitude; and when he reaches that Height, he is faid to Culminate.

The Distance of the Sun, or a Star, from the Horizon, below it, is called its Depreffion.

Imaginary Circles drawn parallel to the Horizon, thro' every Degree of the vertical Circles, are called Parallels of Altitude, or, (by an Arabick Name) Almi

cantars.

7. The Poles of the Ecliptic are generally marked on the Celestial Globe, which fall in the Arctic and Antarctic Circles, at 23 Degrees diftance from the Poles of the Equinoctial.

8. Great Circles cutting the Ecliptic at right Angles, and croffing one another at its Poles, are called Circles of Longitude. And if you imagine other Circles to be drawn parallel to the Ecliptic, thro' every Degree of the Circles of Longitude, they will be Parallels of Latitude upon the Celestial Globe. For Longitude and Latitude

on

on the Celestial Globe, bear juft the fame relation to the Ecliptic, as they do on the Terrestrial Globe to the Equator.

Thus, as the Longitude of Places on the Earth is measured by Degrees upon the Equator, counting from the first Meridian fo the Longitude of the heavenly Bodies is measured by Degrees upon the Ecliptic, counting from the firft Circle, or Line of Longitude, viz. that which paffes thro' the first Point of Aries. And as Latitude on the Earth is measured by Degrees upon the Meridian, counting from the Equator; fo the Latitude of the heavenly Bodies is measured by Degrees upon a Circle of Longitude, counting either North, or South, from the Ecliptic.

The Sun has no Latitude, being always in the Ecliptic: nor do we ufually speak of his Longitude: but his Place in the Ecliptic is expreffed by fuch a Degree and Minute, of fuch a Sign; as 5 Degrees of Taurus, instead of 35 Degrees of Longitude.

9. The Distance of any heavenly Body from the Equinoctial, measured upon the Meridian, is called its Declination. There fore the Sun's Declination, North or South, at any Time, is the fame as the Latitude of the Place on Earth, to which he is then vertical, which is never more than 23Degrees. Therefore, alfo, Parallels of Declination on the Celestial Globe, are the very

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very fame as Parallels of Latitude on the

Terreftrial.

Stars may have North Latitude, and South Declination, and vice verfâ.

The fame Thing which is called Longitude on the Terreftrial Globe, is called right Afcenfion on the Celestial; viz. the Sun, or a Star's Distance from the first Meridian, or that which paffes thro' the firft Point of Aries, counted on the Equinoctial.

Aftronomers alfo fpeak of oblique Afcenfion and Defcenfion; by which they mean the Distance of that Point of the Equinoctial from the first Point of Aries, which, in an oblique Sphere, rifes, or fets, at the fame time that the Sun, or Star, rifes, or fets.

Afcenfional Difference, is the Difference betwixt right and oblique Afcenfion. The Sun's afcenfional Difference, turned into Time, (i. e. reckoning one Degree to be four Minutes, and fifteen Degrees one Hour) is juft fo much as he rifes before, or after, fix a Clock.

The Hemisphere of Stars, which is vifi ble by Night, is continually changing, in a right or oblique Sphere, by reafon of the Sun's apparent Motion round the Ecliptic in a Year.

When the Sun gets fo near a Star, as that the Star is hid in his Beams, it is said to fet

Heliacally:

Heliacally and when after its Conjunction with the Sun, it becomes vifible again, it is faid to rife Heliacally

A Star that rises, or fets, in the Morning, when the Sun rifes, is faid to rife, or Let, Cofmically.

A Star which rifes, or fets, in the Evening, when the Sun fets, is faid to rife, or fet, Achronically.

CHA P. IV.

Of the Divifions of the Heavens, and the Conftellations.

TH

HE Stars appearing to be of different Sizes, fome greater, and fome lefs, Aftronomers have divided them into fix Claffes, or Magnitudes; and the Stars of each Magnitude are diftinguished by different Marks on the Celestial Globe.

They have alfo diftinguifhed the Stars, in refpect to their Situation in the Heavens, into feveral Conftellations, or Afterifms, called Stella Formata, to which they have given Names to fome the Names of Men; to others the Names of Beafts, Birds, and feyeral other Things, as fancy led them. The Images of thofe Animals, and other Things, C 3 from