place to the meridian, and set the index to 12 at noon. Bring the given body to the eastern edge of the wooden horizon, and the index will show the time of rising; and the degree of the equinoctial, that rises with the body, is its oblique ascension; and the distance of the body from the east point of the horizon, is its eastern amplitude. Bring the body to the meridian, and the index will show the time of culminating, or coming to the meridian. Bring it to the western edge of the wooden horizon, and its setting, and oblique descension, and western amplitude will be found in the same manner as its rising, oblique ascension, and eastern amplitude. The number of hours between rising and setting, will be the time of its continuance above the horizon. The sun's oblique ascension and descension, eastern and western amplitude, and time of rising and setting, may be found by this problem, by bringing the sun's place to the eastern or western edge of the wooden horizon instead of the stars. The ascensional difference is found by taking the difference between the right and oblique ascension; and the descensional difference by taking the dif. ference between the right ascension and oblique descension. Required the time of rising, coming to the meridian, and setting; also the oblique ascension and descension, eastern and western amplitude, and continuance above the horizon, of the following stars and planets: 1. Sirius, at London, on February 10. 2. Arcturus, at Newcastle, on September 20. 3. Regulus, at Edinburgh, on October 30. 4. The principal planets, at London, on January 20, 1830. PROBLEM VII. The latitude of the place, the day, and hour being given, to represent the face of the heavens at that time by the globe, and thus to point out the constellations, principal stars, and planets, then visible. RULE.-Mark the places of the planets upon the globe by Problem I. Rectify for the latitude, bring the sun's place to the meridian, and set the index to 12 at noon. Set the globe due north and south by a meridian line, or by a mariner's compass, taking care to allow for the variation. Turn the globe until the index points to the given hour, and the globe will then represent the face of the heavens, shewing all the stars and planets which are above the horizon. If the flat end of a black lead pencil be placed on any star or planet on the globe, so as to point towards the centre, the other end will point to that parti cular star or planet in the heavens. 1. Required the situation of the stars and planets at Newcastle, on the 20th October, 1829, at 7 o'clock in the evening. 2. Required the situation of the stars and planets at London, on the 9th February, 1830, at 9 o'clock in the evening. PROBLEM IX. To find that part of the equation of time which depends on the obliquity of the ecliptic, on any given day. RULE.-Bring the sun's place to the brass meridian. Find the number of degrees between the first point of Aries and the brass meridian both on the equator and on the ecliptic. The difference, reckoning four minutes of time to a degree, is the equation of time. If the number of degrees on the ecliptic exceed those on the equator, the sun is faster than the clock; but if the number of degrees on the equator exceed those on the ecliptic, the sun is slower than the clock. PROBLEM X. To explain by the globe the phenomena of the harvest moon, or the full moon that happens at or near the time of the Autumnal Equinox. RULE.-Elevate the globe for the latitude. Put a patch or mark on the first point of Aries,* and upon every 13 degrees† preceding and following that point, until there be 6 or 7 marks. Bring the mark which is the nearest to Capricorn to the eastern edge of the horizon, and set the index to 12. Turn the globe westward until the other marks successively come to the horizon, and observe the hours passed over by the index; the intervals of time between the marks coming to the horizon will be the daily difference of time between the moon's rising. When the sun is in the beginning of Libra, the moon, at full, will be in or near the beginning of Aries. +The mean motion of the moon is about 13° in a day. The daily difference of time between the moon's setting may be found by bringing the marks to the western edge of the horizon. When there is the smallest difference between the times of the moon's rising, there will be the greatest difference between the times of her setting; and when there is the greatest difference between the times of her rising, there will be the least between the times of her setting. QUESTIONS FOR EXAMINATION. 1. What is meant by the declination of the sun, a star, or planet? 2. Altitude? 3. Antoeci? 4. Perioeci? 5. Antipodes? 6. A right sphere? 7. A parallel sphere? 8. An oblique sphere? 9. Twilight? 2 How do you find the latitude and longitude of any given place? &c. &c. 1. What is the celestial globe? 2. The solar system ?— 3. The sun? 4. What are planets? 5. The primary planets ? How many primary planets are there? Mention them.— 6. What are secondary planets? How many secondary planets are there, and to which of the primary planets do they belong? 7. What is a comet? 8. What are the fixed stars? 9. What is meant by a constellation? 10. Right ascension? 11. Oblique ascension ? 12. Ascensional difference? 13. The latitude of a celestial body? 14. The longitude of a celestial body?— 15. Azimuth? 16. Amplitude? 17. The zodiac? 18. The culminating of any celestial objects? 19. The orbit of a pla net? 20. A digit? 21. The disc of the sun or moon?— 22. The geocentric place of a planet? 23. The heliocentric place of a planet? 24. Apparent time? 25. Equal, mean, or true time? 26. Equation of time? Having the day of the month given, how do you mark the places of the planets on the globe? &c. &c. FINIS. ERRATA. Page 30, line 18 from the top, for Lapari read Lipari. - 63, in the additional towns, after 7. " Belturbet," increase 64, line 5 from the bottom, for Carne read Earne. |