a process which we cannot detail here, an angular quantity, which, after the necessary corrections for the Earth's rotation, and the station of the observers, leads to the horizontal parallax of the Sun; and this is about 8.6 seconds. In what way this parallax enables the astronomer to determine the distance of a planet, we may briefly explain by referring to one of the properties of the triangle. In the annexed figure, the angle at d represents the horizontal parallax of the celestial body d. This angle is a known quantity, and so is likewise the line from c to the centre of the Earth, which is half the Earth's diameter, and is about three thousand nine hundred and sixty miles. Now, if in any right-angled triangle, such as this is, we know the length of the base, and also the value of the angle opposite to it, we can deduce the length of the sides; by which means we obtain the distance of the planet d from the centre of the Earth. Some years ago M. Schröeter, an eminent astronomer of Lelienthal, made a continued series of observations on the planet Venus, for a period of ten years; and his labours led to many remarkable discoveries. He found himself able to determine that there were mountains on the surface of that planet, analogous to those on the surface of the Earth; and that the actual height of some of them amounted to 22.05 miles. Three of them he found to be of the respective heights of 18.97, 11-44, and 10.84 miles. He also perceived evident indications that Venus was surrounded by an atmosphere, which is said to be fifty miles in length. This planet seems to be composed of matter, which is somewhat denser than the matter of the Earth. CHAPTER VI. THE EARTH. ITS FORM. CENTRIFUGAL FORCE. POLES. PERIHELION AND APHELION. THE YEAR-TROPICAL AND SIDEREAL. DIURNAL REVOLUTION. SIZE AND DENSITY OF THE EARTH. THE MOON-GENERAL PHENOMENA OF. THE MONTH AS DETERMINED BY THE MOON. VIEW OF THE EARTH TO THE MOON. LUNAR DAYS AND SEASONS. LIBRATION. THE HARVEST MOON AND THE HUNTER'S MOON. NODES. DISK. PHASES OF THE MOON. ECLIPSES OF THE SUN AND MOON. THE EARTH. What if the Sun Be centre to the world, and other stars Incited, dance about him various rounds? Their wandering course now high, now low, then hid, In six thou seest, and what if seventh to these MILTON'S Par. Lost, b. viii. We have now arrived at the third planet in the order of distance, the Earth, on which we dwell: that habitation which, though it may appear so vast-so mighty. -to our gaze, is but a speck in the great scheme of the universe. Could we but travel into space, and view the solar system as a connected whole, how small would * The annual, diurnal, and libratory motions, explained hereafter. our Earth appear, and how unworthy of the boastful importance which we are apt to attach to it! If there be inhabitants on any of the exterior planets, they see the Earth merely as a small star, shining by the light which she receives from the Sun, and which she reflects from her own surface. That the Earth is round the proofs are many and easy: for, in addition to the gradual appearance, from the top downwards, of a ship coming into port, and the fact of the world having been sailed round, which amounts to practical conviction,-yet, as this sailing has always been in the direction of east and west, the Earth might be cylindrical, and this eastern and western circumnavigation still have taken place; but, in sailing southward, we observe that the fixed stars in the northern heaven sink down towards the horizon, and the southern stars keep on rising in the sky; the reverse taking place as we return northward. This circumstance is beautifully alluded to in the Lusiad of Camoëns, a Portuguese poem, relating to the discovery of India. O'er the wild waves as southward thus we stray, Rolled o'er our heads, and poured the downward ray, Boötes' shining car appears no more: For here we saw Calisto's star retire Beneath the waves, unawed by Juno's ire. The latter part of this quotation implies, that when |