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lar ridges of mountains, and insulated mountains rising from a level surface- an idea of the shadows and circumstances by which these objects are indicated should be previously communicated. This may be done by means of a saucer, the top of a small circular box, or any other object which may represent a plain surrounded by a circular ridge. In the middle of any of these objects may be placed a small peg to represent a mountain. Then placing a candle at the distance of a foot or two, so as to shine obliquely upon the objects, the inside of the circular dish farthest from the candle will be seen enlightened, while a considerable portion of the bottom will be covered by the shadow thrown upon it by the side next the candle, and the shadow of the peg will be seen verging towards the enlightened side. This previous exhibition will give them an idea of the form of some of the mountains and vales on the lunar surface, and enable them to appreciate the nature of those striking inequalities which appear near the boundary between the dark and enlightened parts of the moon. Other objects which diversify the moon's surface may be represented and illustrated in a similar manner, and sufficient time should be allowed to every observer for taking a minute inspection of all the varieties on the lunar disk. The solar spots may be viewed with ease, by interposing a coloured glass between the eye and the image of the sun; but, in looking through the telescope in the ordinary way, they can be perceived by only one individual at a time. In order to exhibit them to a company of 30 or 40 persons at once, the image of the sun may be thrown on a white wall or screen. I have generally exhibited them in the following manner. To a 3 feet Achromatic telescope, I apply a diagonal eye-piece, which has a plain metallic speculum placed at half a right angle to the axis of the telescope. By this eye-piece, after the room has been darkened as much as possible, the image of the sun and his spots is thrown upon the roof of the apartment, which forms a beautiful circle of light, and exhibits all the spots which then happen to diversify his surface. His apparent diurnal motion is also represented, along with the motions of any thin fleeces of clouds which may happen to cross his disk. In this way, too, the proportional magnitudes of the spots may be measured, and compared with the diameter of the sun, and, of course, their real magnitudes ascertained.

In illustrating the phenomena of the planetary system by means of orreries, planetariums, and lunariums, great care should be taken to guard the young against the false and imperfect conceptions of the magnitudes and distances of the planets, which such instruments have a tendency to convey. No orrery, of a portable

size, can represent, at the same time, both the proportional distances and relative magnitudes of the different planets. Even those large machines designated Eidouraniums and Transparent Orreries afford no correct views of these particulars; and some of them convey very erroneous and distorted conceptions of the relations of the solar system, where it is the chief design to dazzle the eye with a splendid show. In some of these exhibitions I have seen the stars represented as if they had been scattered through different parts of the planetary system. An orrery representing the proportional distances and magnitudes of the sun and planets would require to be more than three miles in diameter; and, even on this scale, Jupiter would be less than 3 inches diameter, the Earth a quarter of an inch, or about the size of a small pea, and Mercury only about the dimensions of the head of a small pin, while the sun would require to be represented by a ball 30 inches in diameter—in which case all the planets would be invisible from the centre of the system. To correct, in some measure, the erroneous ideas which a common orrery is apt to convey, the magnitudes and distances should be separately represented. Suppose a celestial globe, 18 inches in diameter, to represent the Sun, Jupiter will be represented by a ball about 14 inch diameter, Saturn by one of 13 inch, Herschel by one of about inch, the Earth by a ball of inch, or somewhat less than a small pea, Venus by a ball of nearly the same size, Mars by a globule of about inch, Mercury by a globule of, and the Moon by a still smaller globule of inch in diameter. These three last might be represented by three different sizes of pin-heads. When balls of these sizes are placed adjacent to an 18-inch globe, and compared with it, an impressive idea is conveyed of the astonishing magnitude of the sun, which is 500 times greater than all the planets, satellites, and comets, taken together. The proportional distances may be represented as follows. At one end of a table 9 feet in length, fix a ball upon a pillar to represent the sun; at 2 inches from the sun's ball, place another to represent Mercury; at 3 inches, Venus; at 5 inches, the Earth; at 71⁄2 inches, Mars; at 25 inches, Jupiter; at 47 inches, or about 4 feet, Saturn; and, at 95 inches, or about 8 feet from the sun's ball, place one to represent Herschel. This will convey a pretty correct idea of the proportional distances from the sun of the principal primary planets. The distances of Ceres, Pallas, Juno, and Vesta, might likewise be represented, if judged expedient; but as their orbits are more eccentric than those of the other planets, and some of them cross each other, they cannot be accurately represented. When orreries or telescopes cannot be procured for exhibiting the

celestial motions and phenomena to which I have alluded, some of these objects, such as the rings of Saturn, the belts and moons of Jupiter, the phases of Venus, the Moon, and some of the constellations, may be represented in a dark room by means of the phantasmagoria. But the representations made by this instrument form but a rude and paltry substitute for the exhibitions presented by the orrery and the telescope, and need never be resorted to, except for amusement, where these instruments can be obtained.

It might next be expedient to communicate to the pupil an idea of the nature of a parallax, to prepare him for understanding the mode by which the distances and magnitudes of the heavenly bodies are ascertained. This might be done by fixing a pole or staff, with a pointed top, in a garden or large area, opposite a wall or hedge, F G, Fig. 1, and, desiring one of the pupils to take his station at A, and another at B, and to direct their eyes to the points on the wall which appear in a line with the top of the pole, when the one stationed at A will perceive it to coincide with the Fig. 1.

point C, and the other stationed at B will perceive it at D. They may be told that CD is the parallax, or the difference of the apparent place of the pole P, when viewed from the positions A and B, which is measured by the angle CPD; and that, if the distance between A and B were measured, and the number of degrees or minutes in the angle CPD or A PB ascertained, the distance between the pole and any of the stations can be easily determined. This may be easily applied to the case of the heavenly bodies by means of such a diagram as Fig. 2, where HIK represents the Earth, M the Moon, P a planet, and S T a quadrant of the starry heavens. It is evident, that, if the moon be viewed from the surface of the earth at H, she will appear in the

heavens at the point a; but if she be viewed from the centre C, she will be seen at the point b, the angle a M b being the angle of parallax. This angle being found, which is the same as the

K

angle H M C, and the base line HC, or the earth's semidiameter being known, which is nearly 4000 miles-the length of the line H M, or the distance of the moon, can be easily determined. It may be proper also to state that the farther any heavenly body is distant from the earth, the less is its parallax. Hence the parallaxes of the sun and planets are all much less than that of the moon, which is the nearest celestial body to the earth. Thus, the parallax c d of the planet P is less than that of the Moon, M, and the same principle likewise holds true with respect to all terrestrial objects. This subject may soon be rendered quite plain to the pupil, by familiar illustrations, in connection with a few instructions on the nature and properties of triangles, and the first principles of trigonometry.

I have been somewhat particular in some of the hints thrown out above, because it is of some importance that the young should have clear and impressive conceptions of every object presented to their view, in every step of their progress on this subject, and

not depend merely on the assertions or the positions announced by their teachers; and because such a train of observations and experimental illustrations has seldom been attended to, in attempting to convey to the juvenile mind a popular view of the leading facts of astronomy. After the pupil has acquired a knowledge of the subjects to which I have adverted, an intelligent teacher will find little difficulty in gradually unfolding to him the doctrines and facts in relation to solar and lunar eclipses-the tides-the form of the planetary orbits-the nature of refraction-the divisions of time-the mensuration of the earth-centrifugal and centripetal forces—the circles of the celestial sphere-and various other particulars connected with astronomical science.

In illustrating the principles and exhibiting the objects of astronomy, the pious and intelligent teacher will have frequent opportunities of impressing upon the minds of his pupils the most sublime ideas of the Perfections of the Creator, and of the Extent and Grandeur of his Empire, and of inspiring them with Love, Admiration, and Reverence; and such opportunities ought never to be neglected. When descanting on the number and magnificence of the celestial worlds, he may very appropriately take occasion to impress them with the idea of the littleness of this earth, and its comparative insignificance, when placed in competition with the numerous and more resplendent worlds and systems which compose the universe; and, consequently, with the folly and madness of ambition, and of all those warlike schemes and ferocious contentions, of which our world has been the melancholy theatre. He may occasionally expatiate a little on the folly of pride, and its inconsistency with the character and circumstances of man, when we consider his comparative ignorance, and the low station which he holds in the scale of creation —and the reasonableness of cultivating a spirit of humility in the presence of that Almighty Being whose "glory is above the heavens,” and “ whose kingdom ruleth over all," when we consider, that, when compared with the myriads of more exalted intelligences that people the universe, we are only like a few atoms in the immensity of space. He may direct their attention to the infinitely diversified scenes of grandeur and felicity which the universe must contain, since its range is so extensive and its objects so magnificent; and to the evidence which these facts afford, that the Creator has it in his power to gratify his rational offspring with new objects, and new sources of enjoyment, during every period of infinite duration.—In short, he may excite them, from such considerations, to aspire after that more glorious state of existence where the works of Omnipotence will be more fully un