The diftance of any heavenly body from the equinoctial, menfured upon the meridian, is called its declination.

The fun's declination either north or fouth, is the fame as *** latitude of the place to which he is then vertical. Therecre, all parallels of declination on the celeftial globe are the fame as parallels of latitude on the terreftrial.

That which is called longitude on the terreftrial globe is called RIGHT ASCENSION on the celestial, namely, the distance of the fun or ftars from the firft point of Aries, counted on the equinoctial. Aftronomers also speak of oblique afcenfion and defcenfion, by which is meant the distance of that point of the equinoctial from the first point of Aries, which rifes or fets at the fame time that the fun or ftar rifes or fets. Or thus, the right efcenfion of the fun or of a star is that point of the equinoctial which comes to the meridian with the fun or ftar: oblique af cenfion is that point of the equinoctial which rifes or fets with the ftar. Afcenfional difference is the difference between right and oblique afcenfion. The fun's afcenfional difference turned into time, is just so much as he rifes before or after fix o'clock.

The celeftial globe is rectified, when it is put in that position in which it may represent exactly the apparent motion of the heavens. As that pofition varies in different places according to their different latitude; therefore, to rectify the globe for any place, is to elevate the pole of the celeftial globe the fame number of degrees and minutes above the plane of the horizon as the latitude of the place is. Thus the latitude of London being 51 degrees, let the globe be moved till the meridian cut the plane of the horizon in that point; bring the fun's place in the ecliptic to the meridian, make the hour-index point to the most elevated 12, or xii at noon, and fet the meridian of the globe north and fouth by the compafs, and the globe will be rectified.

That parallel to the equinoctial which divides the stars that never fet to us from thofe that do, is called the circle of perpetual apparition; the parallel on the other fide of the equinoctial which divides the ftars that never rife from those that do, is called the circle of perpetual occultation.

The right afcenfion and declination of the fun, or of any given ftar, is found after the same manner as the longitude and latitude of a place upon the terrestrial globe.

Bring the fun's place to the meridian, and that point of the equinoctial which is under the meridian will fhew the fun's

right afcenfion; thus, on the 11th May, the right afcenfion of the fun will be found to be 47 degrees 10 minutes. Bring the fun's place to the western edge of the horizon, and the degree of the equator cut by the horizon is his oblique defcenfion; bring it to the eastern fide, and you will there find his oblique afcenfion.

So, bring the given ftar to the meridian, and the degree under which it lies is its declination; and the point in which the meridian interfects the equinoctial is its right afcenfion; thus the declination of Arcturus is 20 degrees 20 minutes north; his right afcenfion, 211 degrees. So the declination of Sirius is 16 degrees 30 minutes fouth; and the right afcenfion 98 degrees 20 minutes.

If the right afcenfion and declination of a ftar be given, its place is eafily found. Thus, fuppofe the right afcenfion of Aldebaran to be 65 degrees 30 minutes, and its declination to be 16 degrees north; then turn the globe about till the meridian cut the equinoctial in 65 degrees 30 minutes, and under the 16th degree of the meridian, on the northern part, you will observe Aldebaran, or the Bull's eye.

The time of the rifing, fouthing, fetting, amplitude, &c. of any ftar in a given latitude and day of the year may be thus found:- Let it be required to know at what time the Pleiades or seven stars rife, fet, &c. in the latitude of London on the 11th of May. The globe being rectified for the latitude of London, and the fun's place for the given day, with the hour-index pointed to twelve, turn the globe about till you bring the Pleiades to the eaftern fide of the horizon, and the index will point to 34 degrees 45 minutes, the time of their rifing in the morn ing. Then bring the faid cluster of ftars to the meridian, and the index will point to about after xii. for the time of their culminating or being upon the meridian: bring them to the weftern fide of the horizon, and the index will point to viii. 40 minutes, which fhews the time of their fetting in the evening that day. It will alfo appear on the circle of the horizon, that they rife with about 40 degrees of amplitude to the north, and fet with the fame amplitude from the weft.

To find what conftellation any remarkable star in the firmament belongs to,

Bring the fun's place in the ecliptic for that day to the brafs meridian, and fet the horary index to that xii. which is most elevated; the celeftial globe being rectified to the latitude, turn the globe till it points to the prefent hour; and by the help of the mariner's compafs, and attending to the variation, which at London is

nearly

nearly 24 degrees from the north, weftward, fet the north pole of the globe towards the north pole of the heavens. The ftar upon the globe (if you conceive yourself in the centre,) which directs towards that point in the heavens in which the ftar you want to know is feen, is the ftar required. At the fame time, by comparing the stars in the heavens with thofe upon the globe, the other stars and their conftellations may be easily known.

To represent the face of the heavens on the globe at a given hour on any day of the year,

Rectify the globe to the given latitude of the place, fetting it due north and fouth by the needle, with the hour-index pointed to xii; then turn the globe on its axis till the index points to the given hour of the night; then the upper hemifphere of the globe will reprefent the vifible face of the heavens for that

time.

Ancient authors mention three forts of rifings and settings of the fixed stars, called poetical rifings and fettings, because chiefly taken notice of by the ancient poets.

When a star rifes or fets at fun-rifing, it is faid to rife or fet cfmically. When it rifes or fets at fun-fetting, it is faid to rife or fet achronically. When a ftar firft becomes vifible in the morning, after being for fome time so near the fun as to be hid by the fplendor of his rays, it is faid to rife heliacally; and to fet heliacally, when approaching towards the fun, it begins to be immerfed in, or hid by, his rays, and ceases to appear above the horizon after fun-fet.

The heavens are bespangled with stars as much in the day time as in the night, only the ftars are rendered invisible to us by the light of the fun. At the bottom of a deep pit, however, we can fee them with the naked eye. When the fun is about 12 degrees below the horizon, ftars of the first magnitude be- . come visible; at 13 degrees, thofe of the fecond; at 14 degrees, those of the third; at 15 degrees, thofe of the fourth magnitude appear; and at 18 degrees all the reft. The stars difappear in the fame manner before fun-rifing. Hence allowance must be made for these variations in computing the time of the cofmical, achronical and heliacal rifing and fetting of the ftars.

To find the time when any planet rifes, fets or culminates at any given place and time,

Find the place of the planet for the day in fome ephemeris or almanack, mark its place on the ecliptic; then elevate the pole to the given latitude, bring the fun's place to the meridian, and fet the index to xii noon; then turn the globe till the marked

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degree of the ecliptic comes fucceffively to the eastern horizon, to the meridian, and to the western horizon; and the index will, in these respective fituations, fhew the hour of the planets rifing, culminating and fetting.

On the celeftial globe may be explained the equation of time, the preceffion of the equinoxes, the phafes of the moon, the tides, the motion of comets, &c. for the illuftration of which the learner is referred to Adams on the globes, and other larger works on this fubject.

Of the TERRAQUEOUS GLOBE and its COMPONENT

Parts.

This earth, as being divided into land and water, is called the Terraqueous Globe. The land comprehends every thing on and below its furface; the water, all liquids and fluids.

The furface of this globe is found almoft every where covered with a blackish mould, properly termed the ground, or the foil; of a different thicknefs and confiftence in different places, producing vegetables of various kinds for the fuftenance of animals, and again receiving the fubflance of animal and vegetable bodies when diffolved, Plin. ii. 63. Thefe vegetables are generally of a green colour, the moft delightful to the fight, and beautifully diverfified.

The furface of the earth is ufually interfected with hills and dales, with fprings, and lakes, and rivulets; fometimes with a craggy mountain, a rapid torrent, or the fpreading ocean.

Below the furface we find various beds or layers of different fubftances, fometimes interrupted with dreadful chafms or fiflures, as in the Alps and Andes, and with caves or caverns, which are common in most countries.

All bodies dug up from below ground are called fails, from a mine, minerals; but the word minerals is fometimes taken in a more limited fenfe, to denote thofe bodies which may be melted, but not malleated or beaten out with the hammer. Thus all metals are minerals, but all minerals are not metals. A defcription of the fituation of the bodies which are found below ground is not improperly called fubterraneous geography.

How the land and water were at firft feparated from one another, and how the different parts of the earth were arranged in their prefent form, although it has often exercifed the ingenuity of learned men in their various theories of the earth, as they are called, yet ftill remains as much unknown as what kind of fubftances

fubftances exift towards its centre. From fhells and other marine substances being now found at a distance from the sea, and even on the tops of mountains, it appears that fuch places have at fome time been covered with water. From the appearance of certain rocks and metallic fubftances, fome suppose this globe to have once been in a state of fufion. The interior part of the earth is found to confift of feams or layers of different substances lying parallel to each other, and often the one above the other. Seneca obferves that light metals are found near the furface, and heavier metals farther down, ep. 23. & 90. Hence fome naturalifts imagine that the gravity or denfity of bodies increases as they approach nearer the centre. This, however, is

not always the cafe; for layers of ftone are often found above. the lighteft foils, and the fofteft earths under the hardeft bodies. Gold, too, is frequently found in loofe earths on the furface, even on the tops of mountains.

But our knowledge on this fubject extends only a very little way; the deepest mine known, which is thought to be that at Cotteburg in Hungary, not reaching farther than about 3000 feet deep. All beyond this is mere conjecture; whether we fuppofe the globe to confift of water, as Burnet; of glafs, as Buffon; of heated iron, with Whiston; or of volcanic matter, with Kircher.

The ancient philofophers entertained different opinions concerning the original formation of the world; fome afferting the eternity of matter, out of which all things were formed, as Democritus and Ariftotle; others, that the world was made out of nothing, and is conftantly preferved by the Supreme Being, as Pythagoras and Plato, Plutarch. de placit. Phil. ii. 4.: Senec. 2 Nat. praf. But Cicero makes the opinion of Plato fimilar to that of Ariftotle, Acad. iv. 37.

There was the fame diverfity of opinion concerning the component parts of bodies, or the first principles of which they are compofed, Ibid.

Thefe were thought by Ariftotle, and most of the ancient philofophers, to be earth, water, air, and fire; hence called the FOUR ELEMENTS. But Leucippus, Democritus and Epicurus, fuppofed all bodies to confift of certain fmall folid particles, called corpufcles or atoms; which doctrine, with a small variation, was adopted by Des Cartes.

Modern chemifts (for fo thofe who examine the nature of bodies are called, by à name unknown to the ancients, and of which the origin is uncertain,) have eftablished various principles of nature, as they are termed: fome, falt, fulphur, mercury,

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and