curve. The two bright stars in the head, ẞ and y Draconis, are about as far from Polaris the other side of the meridian, as the Pointers are on the east. Continue the line formed by the last two stars in the tail of the Great Bear about five times their distance, and it will pass near a bright red star (which will be below the horizon, however, at the time we are supposing): this is Arcturus in Boötes. The bright star called Cor Caroli may be found in line with a in the tail of Draco, and in the tail of Ursa Major at the time we are supposing, it will be just above the horizon in the N.N.E. Cassiopeia will be near the zenith directly opposite to the Great Bear, the Pole Star being nearly equidistant from both. The line which is formed by the Pointers and Polaris being continued will run between Cepheus and Cassiopeia; the former adjoining Draco. The same line continued beyond Cassiopeïa will pass by ẞ and a Pegasi; these two, with a Andromeda andy Pegasi, form an irregular square. The most northerly forms the head of Andromeda ; the opposite one is called Markab; the other two, y and B Pegasi, are Algenib and Scheat. The diagonal of this square being continued toward the north will meet ẞ and y Andromeda and a Persei; this last, at the time we have supposed, being very near the zenith. These seven stars, it will be remarked, are not unlike the constellation of the Great Bear on a large scale, and in a reversed order. Join a and y Ursa Majoris: when prolonged, this line will reach a Persei; and, further on, Algol, in Me dusa's head, a star rendered singular from its constantly varying its brilliancy every three days. Produce a line formed by joining y and Pegasi towards the north, it will pass through the centre of Cygnus. The bright star Vega, or a Lyræ, will be below Cygnus, towards the north; on the other side, lower down towards the horizon, Delphinus will be setting due west. Gemini will be found by joining o and ẞ Ursæ Majoris, and producing it south. The two principal stars are Castor and Pollux. Facing the S.E., on the day and hour in question, you will have before you the most splendid constellation in the heavens, Orion, with his belt and sword; the former being three bright stars at equal distances. The line of these three continued some distance to the south will point to a Canis majoris, or Sirius, the brightest star in the heavens. Above Orion, to the westward, will be the red star Aldebaran, in the eye of Taurus; in the neighbourhood of which are the two beautiful clusters, the Hyades and Pleiades these latter have retained till the present time the names by which they were known to the poet Homer 950 years before the Christian era. See the Odyssey, v. 121 and 271. SECTION V. THE APPARENT MOTIONS OF THE HEAVENLY BODIES. STATIONARY, DIRECT, AND RETROGRADE APPEARANCES OF THE PLANETS GEOCENTRIC AND HELIOCENTRIC LONGITUDE- TRANSIT, CONJUNCTION, OPPOSITION, OCCULTATION. 247. WERE our appointed dwelling-place in the centre of the system, nothing could exceed the grandeur of the celestial movements contemplated from that position. All the planets might then be seen performing their annual courses in circles around us; the slightest disturbance or alteration in the inclination of their orbits would instantly be detected: in short, nowhere would astronomy be studied with such advantage as in the central orb of the sun. The next eligible post, could such a one be obtained, would be some fixed point within the system, where, although the celestial motions would be distorted, yet we should be tolerably well able to reduce them to what they would appear to an inhabitant at the centre. But our position is far inferior to either of these we are placed on a planet midway between the centre and the circumference of the system, which planet is itself in motion; and hence, in every observation which we make on the movements of any other heavenly body, we must make an allowance for our own motion, which is ever rapid and unceasing. Moreover, our position is never, so to speak, above the other members of our system, from whence we could, as it were, look down upon their orbits; on the contrary, our planet revolves in almost the same plane with the others, and hence the orbit is, in the instance of an inferior planet, presented to us edgewise; that is, it is projected among the fixed stars in a line, or in a very eccentric ellipse not much differing from a straight line; precisely as an iron hoop, held so as for one side to be hidden, or nearly so, by the other, would appear to an eye situated in its plane. It will be immediately perceived that the study of apparent motions, and of the laws by which the true motions may be deduced from the apparent, is of the utmost consequence in astronomy. A few ideas on this subject will be as much as we can present, consistently with the plan of this work. 248. If we suppose the earth for a time to be stationary in its orbit, a planet nearer to the sun than it during one entire revolution would appear to us to vibrate on each side of that luminary, to approach him, pass by him, and having reached its limit on the other side, to return, and arrive at the point from whence it set out. On the same supposition of the fixedness of the earth, a planet more distant than itself from the sun would appear to revolve round it; although, as its distance would at one period be much greater than at another, its apparent diameter would be less in the former position than in the latter. 249. Let y, in fig. 16, Plate III., be such a position of the earth, m a superior planet, the dotted line its orbit round the sun s; ahgfx the orbit of an inferior planet. By imagining the eye at y, the phenomena described will be immediately understood. The inferior |