revelation. Between the first creation of the earth and that day on which it pleased God to place man upon it, who shall dare to define the interval ?" 1 In the existing creation, each considerable region has certain tribes of animals in common with other regions, and certain tribes peculiar to itself. The same division of zoological life into distinct provinces is found to have prevailed to some extent in ancient times. In the extinct Faunas of America and Europe of corresponding age, there are some species common to both; but the majority have merely such a degree of resemblance as constitutes them the "analogues" or representatives," the one of the other. The number of fossil species of animals known, of all kinds, exceeds 20,000. C. M. 1 Discourse on the Studies of the University, by the Rev. ADAM SEDGWICK, Woodwardian Professor, Trinity College, Cambridge. PART I.-THE THREE BODIES. 1. THE EARTH,-SYMBOL . Shape and size, approximately, sphere 8000 miles in diameter. Shape and size, accurately a spheroid, with Polar dimensions = 7898 miles. Equatorial dimensions = 7924 miles. Mean density, i.e. specific gravity = 5.67, distilled water being = 1. Force of gravitation at the surface = 16 feet movement in 1st second. Force of gravitation at the distance of Moon = 0.004 feet in 1st second. Rotation on axis, measured by the Sun, or solar day, =24 hours solar time. Rotation on axis, measured by the Stars, or sidereal day, =23h. 56m. 4.0906s. solar time. Inclination of axis to plane of orbit, or " obliquity of ecliptic," 23° 27′ 56.5." = Annual diminution of do., = 0.458". Centrifugal force at equator = 0.00346. Light, derived from the Sun. Light occupies in its passage from Sun to Earth 8m. 13.3s. Orbitual motion of Earth in that space of time, and conse quent error in apparent place of Sun, called "aberration of light," = 20-25", consequently Velocity of light 192,000 miles in 1 second. = Precession of the equinoxes in length in one year, = 50·1. Complete revolution of equinoxial points = 25,868 years. Constitution, rocky mass cooling down by radiation from a primitive molten condition. Condition of surface-much diversified by water and dry land, and their actions upon each other. Atmosphere-height 50 miles. Atmosphere-pressure = 15lbs. on square inch. Atmosphere-maximum effect of refraction at the horizon in distorting the appearance of heavenly bodies = 34' 7". Atmosphere-clouds, height of the Denser, under 0.5 miles; of the 2. THE MOON,-Symbol, (. Shape, spherical. Size 2160 miles in diameter. Mean specific gravity (cubic foot of material) = 0.619. Illuminating power (Moon full, and at mean distance), by light reflected from the Sun, = 1 wax candle at 12 feet distance. Brightness (Sun unity) = 0·000033. Greatest distance = 250,000 miles. Mean synodical revolution, or that which determines the phases, 29.53 days. = Mean sidereal revolution, i.e. the return of the Moon to the same place among the stars, = 27.32 days. Mean motion in a solar day = 13° 10′ 15". Inclination of axis to plane of orbit = 1° 20' 11". Apparent diameter when nearest to us = 33′ 31.1". Apparent diameter, mean distance, 31′ 7.0". = Apparent diameter farthest off = 29′ 21.9". Mean parallax = 57' 0-9". Revolution on axis = time of revolution round Earth. Constitution, rocky, volcanic, mountainous, perfectly dry, and long since cooled down from a state of melting heat. Condition of surface, unchanging. Atmosphere, inappreciable, and clouds, none: so that with like illumination from the Sun, the mountains and valleys are always equally well seen in the telescope. e |