What is a year?

What is a true solar year?

What is an astronomical year, and how is it di

vided?

What is a tropical year, and what is the length of it?

What is a sidereal year, and what is its duration? What is a civil year, and how is the American

civil year divided?

How many days does the common civil year consist of, and what is the duration of the bissextile or leap year?

CHAPTER VIII.

Positions of the Sphere. Names assigned to Persons from their different situations on the Globe, &c.

1. Position of the sphere, is its situation with respect to certain circles on the surface of the earth and the horizon. There are principally three positions of the sphere; right, parallel, and oblique.

2. A right sphere is that position of the earth where the equator passes through the zenith and nadir, the poles being in the rational horizon.

The inhabitants who have this position of the sphere live at the equator; they have therefore no latitude, nor no elevation of the pole. All the heavenly bodies will appear to revolve round the earth from east to west, in circles parallel to the equinoctial, according to their different declinations; one half of the starry heavens will be constantly above the horizon, and the other half below; and the sun always rises at right angles to their horizon, making their days and nights of equal length at all times of the year, because the horizon bisects the circle of diurnal revolution; so that the stars will be visible for twelve hours, and invisible for the same space of time.

3. A parallel sphere is that position of the earth where the equator coincides with, and all its parallels are parallel to the horizon.

Hence, the poles of the world are in the zenith and nadir, while all the meridians cut the horizon at right angles. The inhabitents of a sphere in this position, if there are any, live at the poles; they have the greatest possible latitude; and the stars, which are situated in the hemisphere to which the inhabitants belong, never set, but describe circles parallel to the horizon; while those stars of the contrary hemisphere never rise.,

During the time that the sun is describing the northern signs, the inhabitants of the north pole have continual day, and those of the south pole continual night; and while he is describing the southern signs, the inhabitants of the north pole have continual night, and those of the south pole continual day.

4. An oblique sphere is that position of the earth in which the equator and all its parallels are unequally divided by the horizon.

This is the most common position of the sphere, or it is the situation which the earth has with respect to all its inhabitants, except those at the equator and poles.

To the inhabitants of an oblique sphere, the pole of their hemisphere is elevated above the horizon as many degrees as are equal to the latitude, and the opposite pole is depressed as much below the horizon; so that the stars only, at the former, are seen. The sun and all the heavenly bodies rise and set obliquely; the seasons are variable, and the days and nights are unequal.

5. The inhabitants of the earth have different names assigned to them by geographers, according to the several meridians and parallels of latitude they lie under, and are called antæci, periæci, and antipodes.

6. The antaci, or antecians, are those who live under the same meridian, or line of longitude, and have the same degrees of latitude, but the one has north and the other south latitude; as New-York and Cape St. Antonio.

The antæci have noon at the same time, but contrary seasons of the year; so that when it is summer with one, it is winter with the other, &c.; consequently the length of the days with one is equal to the length of the night with the other. They have different poles elevated, and the stars that never set to the one are never seen by the other. 'Those who live at the equator have no antæci.

7. The periæci, or periacians, are those who live under the same parallel of latitude, but under opposite meridians; their difference of longitude being 180 degrees.

The periœci have the same seasons of the year, and aiso their days and nights of the same length; but when it is noon with the one, it is midnight, with the other. Those who live at the poles of the earth, have no periæci.

8. The antipodes are those inhabitants of the earth who live under opposite meridians, and opposite parallels of latitude; their difference of longitude being 180 degrees, and the one having the same degrees of north latitude as the other has of south latitude.

The antipodes are diametrically opposite to each other, the zenith of the one being the nadir of the other, and, consequently, they walk feet to feet; they have the same seasons and length of days and nights; but all of these at contrary times, it being day to the one when it is night night to the other, summer to the one when it is winter to the other, &c.

9. The inhabitants of the earth have also particular names assigned to them from their shadows falling different ways at noon, and are called Amphiscii, Heteroscii, and Periscii.

10. Amphiscii, or Amphiscians, are the people who inhabit the torrid zone; so called, because they cast their shadows both north and south at different times of the year; the sun being sometimes to the south of them at noon, and at other times to the north.

When the sun is vertical, or in the zenith, which happens twice in the year, the inhabitants have no shadow, and are then called Ascii, or shadowless.

11. Heteroscii is a name given to the inhabitants of the temperate zones, because they cast their shadows at noon only one way.

Thus the shadow of an inhabitant of the north temperate zone always falls to the north at noon, because the sun is then directly south; and an inhabitant of the south temperate zone casts his shadow towards the south at noon, because the sun is due north at that time.

12. Periscii, or Periscians, are those people who inhabit the frigid zones, so called because their shadows, during a revolution of the earth on its axis, turn quite round to all points of the compass, without disappearing.

For as the sun does not set to the inhabitants of the frigid zones during several revolutions of the earth on its axis, but moves quite round; so do their shadows also.

These distinctions of the inhabitants of the earth from the direction of their shadows, are of little, or, perhaps, of no importance.

13. The right ascension of the sun, or a star, is that degree of the equinoctial which rises with the sun, or a star, in a right sphere, and is reckoned from the equinoctial point, Aries, round the globe.

14. Oblique ascension of the sun, or a star, is that degree of the equinoctial which rises with the sun, or a star, in an oblique sphere, and is likewise counted from the point Aries round the globe.

15. Oblique descension of the sun, or a star, is that degree of the equinoctial which sets with the sun, or a star, in an oblique sphere.

16. The ascensional or descensional difference is the difference between the right and oblique ascension, of the difference between the right and oblique descension; and with respect to the sun, it is the time he rises before six o'clock in the summer, or sets before six in the winter.

17. The longitude of the sun, which is usually called the sun's place in the ecliptic, is reckoned on the ecliptic from the point Aries, eastward, round the globe.

18. The time from the first dawn or appearance of the morning, or between the setting of the sun and the last remains of day, is called the crepusculum, or twilight.

The twilight, it is supposed, usually begins and ends when the sun is about 18 degrees below the horizon; for then the stars of the 6th magnitude disappear in the morning, and appear in the evening. It is of longer duration in the solstices than in the equinoxes, but it is longer in an oblique sphere than in a right one; because, in those cases the sun, by the obliquity of his path, is longer in ascending through 18 degrees of altitude.

19. Angle of position between two places on the terrestrial globe, is an angle at the zenith of one of the places, contained by the meridian of that place, and a vertical circle passing through the other place.

The vertical circle, as has already been observed, may be represented by the quadrant of altitude screwed in the zenith of one of the places, and passing over the other; and the angle of position is usually measured on the horizon, from the elevated pole towards the quadrant of altitude.

20. Rhumbs are the divisions of the horizon into 32 parts, usually called the points of the compass. The ancients, according to Pliny, were acquainted only with the four cardinal points, and the wind was said to blow from that point to which it was nearest.