ILLUSTRATED ASTRONOMY. LESSON XXIII. EARTH AND SEASONS. IAT is the shape of the earth? is round like a globe or ball, a little flatpoles. ts position in the solar system? e third planet from the sun. the mean diameter of the earth? miles. [Equatorial diameter 7,926 miles; er 7,899 miles.] ch greater is the equatorial than the polar diameter ? 27 miles. uses the equatorial diameter to be greater than the polar? aused by the revolution of the earth on its ater portion of the surface of the earth is covered with the earth revolves on its axis, the water recedes from rds the equator, until its tendency to run back towards t balances the effects of the centrifugal force. This uatorial diameter to be greater than the polar. If the top revolving on its axis, the water at the equator would wards the poles, until the earth had assumed the form of r as possible. Thus large portions of land in the torrid re now covered by the ocean, would be left dry, and new 1 islands would be formed.] is the mean distance of the earth from the sun? ■t 95,000,000 of miles. a distance of a planet, is half the sum of its greatest and es.] is the specific gravity of the earth? 5 times the weight of water. (5.48.) at time does the earth revolve on its axis, or perform its ution? 4 hours. (In 23 hours 56 minutes; as seen stars.) causes day and night? 21 A. Twenty-three degrees and a half. (23° 27'.) Q. Is the direction of the earth's axis changed during the year? A. Its change is so slight that it may be considered as pointing to the same place in the heavens. Q. When does the north pole lean directly towards the sun? A. On the 21st of June, called the summer solstice. (See Diagram) Q. How many degrees does it lean towards the sun? A. 23 degrees; and the sun is vertical 23 degrees north of the equator. Q. What seasons does this produce? A. Summer in the northern hemisphere, and winter in the southern. Q. When does the north pole lean directly from the sun? A. On the 22d of December, called the winter solstice. (See Diagram.) Q. When the north pole leans from the sun, what are the seasons? A. Winter in the northern hemisphere, and summer in the southern. LESSON XXV. Question. At what points of the ecliptic is the earth at the time of the solstices? Answer. At the solstitial points. Q. Through how much of its orbit does the earth pass, in moving from one solstitial point to the other? A. One half of its orbit, or from one side of the sun to the other. Q. What are those two points called half way between the solstitial points? A. The equinoctial points. (See Diagram.) Q. Why are they so called? A. Because when the earth is in these points, the light of the sun causes day, and the shade of sun is vertical at the equator, and the days and nights causes night. great a portion of the earth is continually in the light of half; the other half being in the shade of t does the revolution of the earth upon its axis, cause? e succession of day and night. LESSON XXIV. . As the earth turns upon its axis, what effect is produced? -. The sun is continually rising to places in the A continually setting to places in the east. hat time does the earth revolve around the sun, or perform revolution? 365 days 6 hours. v fast does it move in its orbit around the sun? 000 miles an hour. v are the changes of the seasons caused? ey are caused by the earth's axis being inclined f its orbit, and its revolution around the sun. are every where equal. Q. When is the sun at the vernal equinox? Q. When is it at the autumnal equinox ? A. On the 23d of September. Q. Which way does the pole lean when the earth is at the equinoctial points? A. It leans sideways to the sun, the sun being vertical at the equator. Q. When the north pole leans towards the sun, why is summer produced in the northern hemisphere ? A. Because the rays of the sun strike it so directly as to cause many rays to fall on a given surface. Q. When the north pole leans from the sun, why is winter produced in the northern hemisphere? A. Because the rays of the sun strike it so obliquely, that they spread over a greater surface. Q. At what points do the ecliptic and equinoctial intersect each other? A. At the equinoctial points. (See Diagram.) Q. How far are the solstitial points from the equator points? ILLUSTRATED ASTRONOMY. AEROLITES, METEORS, &c. HAT are meteors? hey are luminous bodies seen in the night ough the heavens. re they usually called? ng stars, and sometimes fire-balls. s an aërolite? stone falling from the air. tones ever been known to fall from the air? have, and in great numbers. (See Table.) id Laplace, Olbers, and other astronomers account for these stones? believed that they were ejected from volthe moon, beyond the moon's attraction, and ttracted to the earth. did they account for the meteors? 7 believed them to be gaseous matter colthe upper regions, and ignited by some un ise. t is the present theory in regard to aërolites and meteors? onomers believe that they have the same All meteors produce stones which fall to the earth? ey do not; very few of them are of suffinsity to reach the earth before they are 1. these meteors originate in our atmosphere? e most of them have their origin far beyond sphere. at is the present theory of meteors? tronomers maintain that the planetary regions detached portions of chaotic and unconmatter, and that the earth in its orbit fremeets with such masses. hat effect would be produced by such contact? e matter in its passage through the atmoswould suddenly be ignited and the gaseous consumed, and the mineral portion, if any, be condensed and precipitated to the earth in of a stone. hat is a peculiar characteristic of meteoric stones? ey are all composed of the same minerals and n the same proportions, and are unlike in their ions to any minerals found on the earth. hat does this fact prove? conclusively proves that they have a common Then was the greatest meteoric display ever known? (See 23 Under Tullus Hostilius. Consuls C. Mart. & Torquatus. Year before the defeat of Crassus. Second year of the 78th Olympiad. Year before J. O. 452. In 1510. November 27, 1627. April 6, 1719. In 1658. In 1646. September, 1753. In 1750. September 13, 1768. In 1768. In 1768. July 24, 1790. December 13, 1795. November 7, 1492. One of the instances in the table is of sufficient interest to deserve a notice. A singular relation respecting the stone of Ensisheim on the Rhine, (at which philosophy once smiled incredulously, regarding it as one of the romances of the middle ages,) may now be admitted to sober attention as a piece of authentic history. A homely narrative of its fall was drawn up at the time by order of the emperor Maxthe year of the Lord 1492, on Wednesday, which was Martinmas eve, the 7th of November, a singular miracle occurred; for, between eleven o'clock and noon, there was a loud clap of thunder and a prolonged confused noise, which was heard at a great distance; and a stone fell from the air, in the jurisdiction of Ensisheim, which weighed two hundred and sixty pounds, and the confused noise was, besides, much louder than here. Then a child saw it strike on a field in the upper jurisdiction, towards the Rhine and Inn, near the district of Giscano, which was sown with wheat, and it did no harm, except that it made a hole there; and then they conveyed it from that spot; and many pieces were broken from it, which the landvogt forbade. They, therefore, caused it to be placed in the church, with the intention of suspending it as a miracle; and there came here many people to see this stone. So there were remarkable conversations about this stone; but the learned said that they knew not what it was; for it was beyond the ordinary course of nature that such a large stone should smite the earth from the height of the air; but that it was really a miracle of God; for, before that time, never anything was heard like it, nor seen, nor described. When they found that stone, it had entered into the earth to the depth of a man's stature, which every body explained to be the will of God that it should be found; and the noise of it was heard at Lucerne, at Vitting, and in many other places, so loud that it was believed that houses had been overturned; and as the King Maximilian was here the Monday after St. Catharine's day of the same year, his royal Excellency ordered the stone which had fallen to be brought to the Castle, and, after having conversed a long time about it with the noblemen, he said that the people of Ensisheim should take it, and order it to be hung up in the church, and not to allow any body to take anything from it. His Excellency, however, took two pieces of it; of which he kept one, and sent the other to the Duke Sigismund of Austria: and they spoke a great deal about this stone, which they suspended in the choir, where it still is; and a great many people came to see it." Contemporary writers confirm the substance of this narration, and the evidence of the fact exists; this aerolite is precisely identical in its chemical composition with that of other meteorie stones. It remained for three centuries suspended in the church, was carried off to Colmar during the French revolution; but has since been restored to its former site, and Ensisheim rejoices in the possession of imilian, and deposited with the stone in the church. It may thus be rendered:-"In the relic. NOTE 2. We now come to by far the most splendid display on record; and as it was the third in successive years, and on the same day of the month, it seemed to invest the meteoric showers with a periodical character; and hence originated the title of November meteors. An incessant play of dazzlingly brilliant meteors was kept up in the heavens for several hours. Some of these were of considerable magnitude and peculiar form. One of large size remained for some time almost stationary in the zenith, over the Falls of Niagara, emitting streams of light. The wild dash of the waters, as contrasted with the fiery uproar above them, formed a scene of unequalled sublimity. In many districts, the mass of the population were terror-struck, and the more enlight ened were awed at contemplating so vivid a picture of the Apocalyptic image-that of the stars of heaven falling to the earth, even as a fig-tree casting her untimely figs, when she is shaken of a mighty wind. A planter of South Carolina thus describes the effect of the scene upon the ignorant blacks:-"I was suddenly awakened by the most distressing cries that ever fell on my ears. Shrieks of horror and cries for mercy I could hear from most of the negroes of three plantations, amounting in all to about six or n the night of the 12th and 13th of November, eight hundred. While earnestly listening for the cause, I heard a faint voice near the That was the altitude of the meteors on this occasion? rofessor Olmstead says they were not less than iles above the earth. door calling my name. I arose, and taking my sword, stood at the door. At this moment, I heard the same voice still beseeching me to rise, and saying O my God, the world is on fire.' I then opened the door, and it is difficult to say which excited me most-the awfulness of the scene, or the distressed cries of the negroes. Upwards of one hundred lay prostrate on the ground-some speechless, and some with the bitterest cries, but with their hands raised, imploring God to save the world and them. The scene was truly awful; for never did rain fall much thicker than the meteors fell towards the earth; east, west, north, and south, it was the same." nany degrees does the axis of Mars lean towards its orbit? at 30 degrees. (30° 18'.) (See Diagram.) Mars have any change of seasons? seasons are similar to those of the earth, but ice as long. are they longer.? Q. What is their magnitude? A. They are very small. Q. Are all their orbits in the same plane? A. They are not. Their orbits intersect each other in many points.-See diagram. NOTE. Astronomers in comparing the distances of the planets, found that there was a great distance between Mars and Jupiter which did not coincide with the uniformity exhibited by the other planets. This led them to suspect that there was an undiscovered planet circulating in that region, and Baron de Zach went so far as to calculate in 1784-5, the orbit of this ideal planet. So confident were astronomers of use Mars is nearly two of our years in revolv- the existence of a planet, that in 1800, six astronomers, of whom Baron de Zach nd the sun. t is the appearance of Mars when seen with the naked eye? planet from the regions of analogy into the realms of sense; ppears of a red, fiery color. LESSON XXVII. w does Mars appear when viewed with a telescope? was one, assembled at Lilienthal, and formed an association of twenty-four observers, the principal object of which was to use their own language "to force this "but before they had got fully organized, Piazza discovered Ceres; after another year Olbers discovered Pallas, and Juno and Vesta were brought in at intervals of a few years. The search continued fruitless for ten years, it was fairly concluded that this region was exhausted. In consequence of the discovery of four small planets instead of one large planet, the new and somewhat novel idea was advanced by Dr. Olbers, that these bodies were originally united in one planet; but by some internal explosion had been blown in pieces. lines of apparent continents and seas, are dis- This theory has been fully discussed by astronomers from that time to the present, (1860) and is discarded by astronomers generally, in consequence of the discovery of 53 new asteroids since 1845. The following is a list of the names of the asteroids, and date of discovery. Number and Name. Date of Discovery.||Number and Name. Date of Discovery. right spots are seen alternately at the poles. When it is winter, or continual night at the poles. Proserpina Amnhituita 1801, Jan. 1. 1802, Mar. 28. 1804, Sep. 1. 1807, Mar. 20. 1845, Dec. 8. 1847, July 1. 1847, Aug. 13. 1847, Oct. 18. 1848, April 25. 1849, April 12. 1850, May 13. 1850, Sept. 13 1850, Nov. 2. 1851, May 20. 1851, July 29. 1852, Mar. 17. 1852, April 17. 1852, June 24. 1852, Aug. 22. 1852, Sept. 19. 1852, Nov. 15. 1852, Nov. 16. 1852, Dec. 15. 1853, April 5. 1853, April 6. 1853, May 5. 1853, Nov. 8. 1854, May 1. 1854 Mar 1 |