between the polar circles and the poles, the climates there being computed by months. Exactly at the poles the fun is vifible for one half-year together, and not vifible the other. He becomes vifible at the north pole about the 21st March, at mid-day, and continues fo till about the 23d September. The fouth pole in like manner enjoys the fight of him for the other fix months.

HORIZON.] The wooden circle which furrounds the globe is called the horizon, because it reprefents that line which terminates our view. It divides the globe into the upper and lower hemifpheres. The upper is fuppofed to be enlightened by the fun, the other not. The point in the heavens directly over our heads is called by an Arabic word, the ZENITH; and that diametrically oppofite below, the NADIR.

The horizon is commonly diftinguifhed into fenfible and rational or real. The fenfible is the circular line which limits our view; the rational or real, is that which would bound it, if we could fee at once the one half of the globe; but when both thefe are fuppofed to be extended to the heavens the difference between them is trifling, and therefore this diftinction is juftly neglected by aftronomers, who always understand by the horizon, (FINIENS, Cic. divin. ii. 44. vel FINITOR, Senec. Nat. 2. v. 17.), that circle which feparates the vifible hemi fphere of the heavens from that which is not vifible, and which to us is continually changing. It is the rational horizon which is reprefented by the broad wooden circle on the terrestrial globe.

On the horizon are marked the SIGNS, as they are called, or the conftellations of the zodiac; and oppofite to them the months and days of the year which anfwer to them. On the ecliptic are correfpondent marks, by which the fun's place at any time of the year, and the length of the day and night in any part of the earth, may be found. But this, with the ufe of the horary circle, quadrant of altitude, &c. and other geographical problems, as they are called, can beft be shown on the globe itself.

LATITUDE.] The distance of any place, north or fouth from the equator to either of the poles, is called latitude. It never exceeds 90 degrees; and thefe are marked on the brazen meridian. All places under the fame parallel are in the fame degree of latitude, and have the fame feafons, and the fame length of days and nights.

LONGITUDE.] The diftance of any place from another eafl or weft, is called longitude, and is marked on the equator. It never exceeds 180 degrees, which is half the circumference of the globe; because if a place be more than that east of us, we

compute

compute weftwards.Thofe under the fame meridian have the fame longitude, and mid-day at the fame time. The extent of a degree of longitude gradually diminishes as we advance from the equator to the poles.

In computing longitude, geographers formerly used to begin at Ferro, one of the Canary islands, which they called the first meridian; but now they commonly begin at the capital of their own country.

Several commercial ftates have propofed confiderable rewards for the difcovery of a certain method of computing the longitude at fea, which has not yet been discovered.

ZONES.] The earth is divided into five zones or belts, Virg. G. i. 233. Æn. vii. 226.; Ovid. Met. i. 45. The space round the globe between the two tropics is called the torrid zone, 47° broad, which, on account of its heat, was, by most of the ancients, thought to be uninhabitable, Ovid. ib. 49.; between the tropics and the polar circles, the two temperate zones, each 43° broad; and between the polar circles and the poles, the two frigid zones.

Thofe who inhabit the torrid zone, are called by a Greek word AMPHISCII, because at mid-day their fhadow points either north or fouth, according to the place of the fun. When the fun at mid-day is vertical to them, they are called Ascii, becaufe they have no fhadow at all; (LOCA ASCIA, Plin. ii. 73. 1.75-)

Thofe who inhabit the other parts of the earth are called HETEROSCII, becaufe at mid-day their fhadow always points one way north or fouth. Thofe within the polar circles, to whom the fun never fets, are called PERISCII, because their shadow points every way round.

Those who live under the fame meridian, but in oppofite parallels, are called ANTECI; those who live in the fame parallel, but under oppofite meridians, are called PERIECI; and those who live under oppofite parallels and oppofite meridians, are called ANTIPODES, Cic. Somn. Scip. 6.; Acad. iv. 39.; Senec. Ep. 122. All these diftinctions between the inhabitants of the earth with refpect to their fhadow, (oxia, umbra,) and habitation, (xos, domus, vel binok, habitatio,) were known to the ancient geo graphers. Pliny names only the Afcii, but mentions one place in India, where the fhadows at noon in fummer pointed to the fouth, and in winter to the north; and another place, where the fun appeared to rife on their right hand, and the fhadows fell towards the fouth, Plin. ii. 73. f. 75. Thus Lucan speaks of Arabians in the army of Pompey, who wondered that their shadows ne

ver

ver moved to the left, (umbras mirati nemorum non ire finiftras ;) iii. 248. SoPliny, vi. 22. Strabo recounts from Pofidonius and others, the Amphifcii, Heterofcii, and Perifcii; but the laft, he thought, did not pertain to geography, as the places within the polar circles were uninhabitable on account of the cold; ii. fub fin. Achilles Tatius, a mathematician of Alexandria, in his introduction to Aratus, having enumerated all thefe, adds the Afcii, i. e. thofe who have no fhadow. Brachyfcii, i. e. those who have short shadows, Macrofcii, having long fhadows, and Antifcii, having their fhadows opposite to one another, as those in the north and fouth of the tropics, c. 31. To the Antaci, Periaci, and Antipodes, he adds the Synaci, who live in the neighbourhood of one another; c. 30. So Cleomed. i. The Periaci are called by Cicero Obliqui; the Antaci, Averfi; and the Antipodes, Adverfi; Somn. Scip. 6.

When the poles coincide with the horizon, it is called a RIGHT SPHERE; when they are in the zenith and nadir, a PARALLEL SPHERE; when the globe is in any other pofition, an OBLIQUE

SPHERE.

The Manner of finding the Latitude and Longitude of Places.

THE latitude of a place is found by bringing it to the brazen meridian, and observing what degree is marked over it. All places which pafs under the fame point of the meridian, in turning round the globe, have the fame latitude, the fame length of day, and the fame feafons. The longitude will be found marked on the equator, where the meridian of the place croffes it; and all the places, which come under the fame meridian, will have noon and midnight, and all the other hours. of the day and night, at the fame time. When any place is brought under the brazen meridian, and it is fuppofed to be noon at that place, all places 15 degrees eaft of it will have 1 o'clock afternoon, and 15 degrees weft 11 o'clock forenoon: 30° eaft 2 o'clock afternoon, 30° weft, 10 o'clock forenoon, and fo on round the globe. Thus the hour is eafily found in any part of the earth.

If a person fail round the earth eastward, he will gain a day; that is, when he returns to the place he has left, he will reckon the fecond day of any month, when the people of the place reckon the firft. On the contrary, if he fail weft he will lofe a day. Thus fome of our navigators found Europeans keeping Sunday in certain islands, to which the first inhabitants of thofe iflands had failed eaftwards, while the inhabitants of other

iflands at no great distance, to which they had failed weftwards, reckoned the fame day Saturday. Dampier's Voyages.

The longitude is commonly marked eastward from the firft meridian, round the whole globe; but it is usually reckoned one half eastward and the other half weftward; hence on most globes it is marked both ways, the one number above the other.

The bearing or fituation of places with respect to one another is determined by a kind of spiral lines, called rhomb or rhumb lines, marked on the globe, and paffing from one place to another, fo as to make equal angles with all the meridians they cut.

The terreftrial globe is faid to be rectified, when it is placed in the fame pofition in which our earth ftands with respect to the fun. This is always varying according to the different declination of the fun, or his diftance north or fouth from the equator, which on fome globes is fo marked on the brazen meridian, on each fide of the north pole, that by bringing that part of the graduated fide of the meridian, on which the day is marked, to coincide with the broad paper circle, which reprefents the horizon, the globe will be rectified, or in the pofition required. If there are no fuch marks, find the day of the month on which the pofition of the globe is required on the broad paper circle; then find the fame day, or, in other words, the fun's place in the ecliptic, and bring it to the graduated fide of the meridian; and raife the north or fouth pole according to the latitude of the fun's place for that day, fo that the point of the meridian which coincides with the fun's place may be in the zenith, then the globe is rectified, or in the pofition required. Thus we may fee at one view what places of the earth fee the fun, and how long; the places which, in turning round the globe, do not rife above the broad paper circle, or the horizon, never fee the fun, and thofe which do not fink under it never lofe fight of the fun: the height of the fun to each place at mid-day is exactly according to the height of that point of the meridian under which it paffes in turning round the globe. If we bring the place at which we are to the graduated fide of the meridian, and fuppofe it midday at that place, the part exactly under that point of the meridian over which the fun paffes for that day, will then have the fun vertical to it, and all the other parts under the meridian will then have noon, and the fun will appear either north or feuth, higher or lower, according to their refpective latitudes; all the places on the weft fide of the broad paper circle or ho1izon will have the fun rifing, and on the caft, fetting; places

18 degrees below the western femicircle of the horizon will have the twilight in the morning just beginning, and 18 degrees under the eastern semicircle the twilight juft ending, and total darkness beginning.

The length of the day at any place is found by bringing that place to the weft fide of the horizon, and then turning the globe till it reach the eaft fide, and marking the hours on the hour-index or hororary circle, or by counting the meridianal lines between one fide of the horizon to the other.

The terreftrial globe is ufed for folving various other problems, as they are called, the most useful of which may be understood from what has been faid, and for the rest the learner is referred to larger works on the subject.

Hiftorical Account of the Progress and Improvements of ASTRONOMY and GEOGRAPHY.

HE motion of the heavenly bodies has in all ages and nations attracted the attention of mankind. Aftronomy is faid to have been first cultivated by the Chaldæans, the Phenicians, and Egyptians. From them the Greeks derived their first knowledge of this fcience, as of various other things, Herodot. Euterp. 32. To aftronomy is afcribed the origin of feveral fables in their mythology, as of Prometheus, Phaeton, &c.

The first of the Greeks who laid the foundations of astronomy Was THALES, born at Miletus in Afia Minor, b. C. 641, who explained the cause of eclipfes and predicted one, Herodot. i. 7.; Plin. ii. 12. f. 9.; Plutarch. de placit. phil. ii. 24. He taught that the earth was round, and divided it into five zones; he difcovered the folftices and equinoxes, and divided the year into 365 days. Having travelled into Egypt in queft of knowledge, he measured the height of the pyramids from their fhadow, D. Laert. i. 27. He looked upon water as the principle of all things, Cic. Acad. iv. 37.; Nat. D. i. 10. From him that sect of philofophers called the IONIC, derived its origin.

The opinions of Thales were maintained and propagated by his fcholar ANAXIMANDER, born b. C. 610, who is faid to have invented maps and dials, and alfo to have conftructed a sphere; D. Laert. ii. 1.; Plin. vii. 56. He taught, that the fun was a circle of fire, like a wheel, 28 times bigger than the earth. Plutarch. pl. phil. ii. 20.

ANAXIMENES was the fcholar of Anaximander, born b. C. 554. He taught that air is the origin of all things, Cic. Acad.