whole orbit. While the earth, viewed from the sun,
would describe this circle among the stars, the sun, to
us on earth, appears to describe precisely the same
circle, only beginning at the opposite point. For while
the earth actually moves from A to B, the sun appears
to move from c to d; and while the earth moves from
B to C, the sun appears to move from d to a, and so on.
This path or circle, which the earth describes as seen
from the sun, and which the sun appears to us to
describe, is called the ecliptic; and a plane, passing
through this circle, is called the plane of the ecliptic.
(The surface of the paper on which the figure is drawn,
properly represents a PLANE.) The ecliptic, and in
fact all circles, whether great or small, are divided
into 360 degrees (marked ), and each degree into (0
minutes, (marked), and each minute into 60 seconds,
(marked), and so on into smaller divisions. The
ecliptic has another division into 12 signs, containing of
course 30 each.
division into signs, and the
names of the signs are given in the figure, beginning
with Aries, and reckoning through Taurus, Gemini, &c.
Instead of the names of the signs, the characters prefixed
to them in the figure, are often used. These characters
are placed in the ECLIPTIC in the Frontispiece: by
which it may be readily seen in what sign, and nearly in
what part of a sign, is the aphelion of each planet. The
English names of the signs, in order, are the Ram, the
Bull, the Twins, the Crab, the Lion, the Virgin, the
Scales, the Scorpion, the Archer, the Goat, the Water-
Bearer, the Fishes.

Th

The instructer should explain degrees to the pupil; show him, that they are not of any absolute determinate length, but vary as the circle is greater or smaller. This may be readily done by drawing two or three concentric circles, and a few lines from the centre to the outermost circle

12. But the other primary planets, when seen from

the sun, do not describe exactly the same circle among the stars, that the earth does; but are sometimes on one side of the ecliptic, and sometimes on the other. But none of them, except Juno, Pallas, and Ceres, are ever farther distant from the ecliptic than 8°. So that within a zone or belt of 160, (80 on each side of the ecliptic,) the planets, except those just named, are always to be found. This zone is called the Zodiac. It is represented by the dark belt interspersed with stars, in the figure. The inner half represents the part beyond the ecliptic; the outer half, the part on this side. The points, where the orbit of any heavenly body cuts the plane of the ecliptic, are called the nodes of that body. The point, where the body passes from the north side of the plane of the ecliptic to the south, is called its descending node; where it passes from the south to the north, its ascending node.

In order that what has been said may be well understood, it may be necessary for the pupil to go over it again and again. Nothing should be passed over without being understood. Instructers should explain and illustrate what is obscure, and in many cases necessarily so. A familiar illustration will give a pupil a better idea of such things as axis, plane, degree, focus, and many others, than can be done in a dozen pages.

SECT. 2. Of the Sun.

13. The sun is the centre of the solar system, dispensing heat and light to all the various bodies, which continually move round him. Like the Centre of the universe, the sun is constantly imparting of its own to recipient subjects. All the bodies in our system, which revolve round him, impart no rays of their own, but are seen by his light reflected. In like manner in universal nature, we see reflected, the love and wisdom of the Lord. The different distances of the planets from

the sin occasion a reception of different degrees of heat and light. These are received according to the square of the distance of the planet from the sun; that is, they decrease as the square of the distance increases. Thus, if the distance of one planet from the sun be 1, and the distance of another be 2, and of a third be 3, the heat and light received at the first is 1 x 1 = 1, at the second 2 X 24 times less, or, at the third 3 x 39 nine times less, or .

14. The truth of this rule admits of familiar proof. (Pl. II, fig. 1.) Let A be a lamp, BF a square hole cut through a piece of pasteboard, placed at the distance of 1 foot from the lamp. Let the heat and light, which pass through the hole BF, fall upon a surface CO, at the distance of 2 feet from the lamp; it will be seen, that the surface CO is 4 times greater than the hole or surface BF; consequently, the heat and light at any point in CO, is 4 times less, than at a point in BF. But if there be a surface DS, at the distance of 3 feet, instead of CO, it will be found, that the heat and light passing through BF is diffused over a surface 9 times greater than BF; consequently, the heat and light at any point in DS is nine times less, than at a point in BĚ. Thus, as the square of the distance increases, heat and light decrease.

15. The sun does not always exhibit the same appearance. Dark spots are often seen on his disk; and sometimes, spots brighter than the rest of his surface. They appear to cross the disk from east to west; are alternately visible and invisible for the same length of time. Whence it is certain, that the sun turns on his own axis from west to east. The time of his rotation is little more than 25 days. The cause of these spots, which often change their size and figure, is not known.

16. The Zodiacal light is a singular phenomenon, accompanying the sun. It is a faint light which often

appears to stream up from the sun a little after sunset and before sunrise. It appears nearly in the form of a cone, its sides being somewhat curved, and generally but ill defined. It extends often from 50° to 1000 in the heavens, and always nearly in the direction of the plane of the ecliptic. It is most distinct about the beginning of March; but is constantly visible in the torrid zone. The cause of this phenomenon is not known.

In Almanacks, the sun is usually represented by a small circle, with the face of a man in it.

SECT. 3. Of Mercury.

17. Proceeding from the sun, the grand centre of the system, the first planet is Mercury. It revolves round the sun at nearly the mean distance of 37 millions of miles, and completes its revolution in about 3 months. The time, in which it turns on its axis, is about 24 hours. It emits a brilliant white light; but because it is near the sun, and consequently seldom out of twilight, it is not often noticed. Its greatest apparent distance from the sun, or its greatest elongation, is never more than 28°. When viewed through a good telescope, it exhibits all the different appearances or phases, which the moon does, and they are to be accounted for in the same manner. Of this we shall treat hereafter.

18. The distance of Mercury from the sun is to that of the earth nearly as 3 to 8. Therefore the degree of heat and light at Mercury is to that at the Earth, nearly as (8 x 8) 64 to (3 x 3) 9; which is very nearly as 7 to ì. Consequently, at Mercury, heat and light are 7 times greater than with us. Water would there fly off in steam and vapour.

1.