PHOSPHORIC, luminous PLANE of a planet's orbit, is the imaginary surface in which it lies; passing through the centre of the planet it extends indefinitely into the heavens. PLANETARIUM, an instrument made use of for showing the phenomena of the planets. PLEIADES, the seven stars, a prominent cluster of stars in Taurus. POLAR CIRCLES, two small circles drawn round the Earth from east to west, parallel to the Equator, about 23° 28′ from the poles; the northern called the Arctic, the southern the Antarctic circle. POLES of the world, extremities of the Earth's axis, PRECESSION OF THE EQUINOXES, a slow motion of the two points where the Equator intersects the Ecliptic, which are found to move backwards, about 50 seconds a year, and a whole circle in 26000 years. QUADRANT, the fourth part of a circle; or an instrument used for measuring angles and taking the altitude of the heavenly bodies. QUADRATURES, or QUARTERS, those phases of the Moon which take place between the conjunction and opposition, and between the opposition and conjunction. RADIATION, the act of a body diffusing rays all around and from a centre. RADIUS, semi-diameter of a circle. REFRACTION, bending of the rays of light in passing through mediums of different densities. RECTILINEAL, in a right line. RETARDED MOTION, continually decreasing velocity. RETROGRADE, an apparent motion of the planets in some parts of their orbits where they seem to go backwards. REVOLUTION, is that motion by which the heavenly bodies, in a certain time, return again to the same points of their orbits. ROTATION, the motion of any heavenly body round its axis. SECOND, the 60th part of a minute. SIDERIAL DAY, the time which elapses between a star's appearing twice on the same meridian. SIDERIAL YEAR, the time which elapses between the Sun's appearing twice in conjunction with the same star. SOLSTICES, the time the Sun enters Cancer and Capricorn. SPHEROIDAL, approaching to the figure of a sphere, though not exactly round." STELLATED, decked with stars. STATIONARY, that state in which a planet is when it has n apparent motion. STRATA, beds or layers. STYLE, the manner of reckoning time from some particular period or remarkable event. SYZYGIES, the conjunction and opposition of a planet with the Sun. TELESCOPIC STARS, are those which are only discoverable by means of a telescope. TRANSIT, is the passing of an inferior planet over the Sun's disc. TWILIGHT, is that light which precedes the rising, and succeeds the setting of the Sun. UMBRA, the conical shadow of the Earth or Moon in an Eclipse. VERTICAL, directly over head, or in the zenith. ZENITH, that point of the heavens, which is perpendicularly over our heads, ZODIAC, a zone surrounding the heavens, of about sixteen degrees broad; in the middle of which is the Ecliptic; and in which the orbits of all the planets are included except three of the asteroids. ZODIACAL LIGHT, a brightness sometimes observed in the Zodiac, resembling that of the Galaxy. It appears at certain seasons, viz. towards the end of winter, and in spring after sunset; or before his rising in autumn, and in the beginning of winter, resembling the form of a pyramid lying lengthways with its axis along the Zodiac, its base being placed obliquely with respect to the horizon. The cause of this light is yet too imperfectly understood, to pronounce on it with confidence. ZONE, a division of the Earth. There are five zones: one torrid zone, lying between the tropics; two temperate zones, between the tropics and the polar circles; and two frigid zones, between the polar circles and the poles. The questions were intended to exhaust the topics discussed, and with few exceptions, will be found on the pages arith their answers. PROBLEMS ON THE GLOBES, AND USEFUL TABLES PROBLEM I.-To find the Latitude of a place. Bring the given place under the brazen meridian, and the number of degrees on it to which the place corresponds is its Latitude. PROBLEM II.-To find the Longitude of a place. Bring the given place to the brass meridian; and the number of degrees which it cuts on the Equator, will be the Longitude of that place. PROBLEM III. To find the Sun's place in the Ecliptic on any given day. Look for the given day and month, on the wooden horizon, and opposite to the day will be seen the sign and degree in which the Sun is then; and this being noted on the Ecliptic, will give the Sun's place on the day required. PROBLEM IV. To find, at any hour, what o'clock it is at any other place. Bring the place of which the hour is known to the brass meridian; set the index to the given hour. If the place required be now brought under the meridian, the index will mark the hour at the place required. PROBLEM V. To find the time of the Sun's rising or setting for any given day. Rectify the globe for the Latitude of the place you are in; bring the Sun's place for the given day to the brass meridian; and set the index to 12. If the Sun's place be turned to the eastern edge of the wooden horizon, the index will shew the hour of sun-rise; and if it be brought to the western edge, the index will shew the time of sun-set. Twice the hour of the Sun's setting gives the length of the day; and twice the hour of its rising, the length of the night. PROBLEM VI.-Given the day and hour at any place, to find those places where the Sun is then rising or setting, and on the How do you find the Latitude of any place on the globe? What is the Latitude of London ?-of St. Petersburgh ?-of Washington? (See the Tables for correcting the answers given by the Pupils.) How do you find the Longitude? What Is the Longitude of Paris?-of Constantinople of NewYork? (See the Tables that are intended to be a substitute for the usual detail of examples.) How find the Sun's place in the Ecliptic for a given day? How do you find what o'clock it now is in any given place? How can the time of the Sun's rising and setting be known for a given day? meridian, or midnight. 1. Find the place where the Sun is vertical at the given hour. To do this, bring the Sun's place for the given day to the brass meridian; mark its declination; bring the given place to the brass meridian, and set the index to the given hour; turn the globe till the index points to 12; the degree of the Sun's declination for that day shews the place to which it is vertical at the given hour. 2. Elevate the pole as many degrees above the horizon as are equal to the Latitude of the given place; bring it to the brass meridian: the Sun rises then for all places on the western edge of the wooden horizon, and sets at all places on the eastern edge. It is noon at all places under the brass meridian, and midnight at all those under the lower part of this meridian. The morning twilight is beginning in all places 18° below the western semicircle of the horizon; and the evening twilight is ending in all places 18° below the eastern semicircle of the wooden horizon. PROBLEM VII.-To find the Antoci, Perioci, and Antipodes of any place. Bring the given place to the brass meridian, and observe its latitude, then under the same degree of latitude, in the opposite hemisphere you will find the Anteci. Set the index of the hour circle to 12, turn the globe half round, or until the index points to the other 12; then under that degree on the brass meridian, which is the latitude of the given place, you will find the Perioci. Under the same degree of latitude with the given place, but in the opposite hemisphere, you will find the Antipodes. PROBLEM VIII.-To find at what rate per hour the inhabitants of any place are carried, from west to east, by the revolution of the earth on its axis. Find by the Longitude table, how many miles make a degree of longitude in the latitude of the given place, which multiply by 15 for the answer. PROBLEM IX.-Any day being given, to find all those places of the earth where the sun is vertical on that day. Find the If the day and hour are given at one place, how determine where the Sun is then rising or setting or in the meridian ? How do find the Antoci? How the Perioci? How the Antipodes You How can the rate of motion per hour on any given plane be ascertained? What is the rate per hour of New-York? Boston?Charleston, S. C.? Over what places will the Sun be vertical the 27th of January? Over what places the 4th of August ? san's declination (by Prob. III) for the given du, turn the globe round on its axis from west to east, and all the places on the globe, which pass under the degree of the sun's declination on the brass meridian will have the Sun vertical on that day. PROBLEM X.-To find the length of the longest day at any place in the north frigid zone. Find the complement of the latitude of the given place, by subtracting its latitude from 90 degrees; count as many degrees on the brass meridian from the equator towards the north pole, as are equal to the complement of the latitude, and mark where the reckoning ends; turn the globe on its axis, and observe what two points of the ecliptic pass under the above mark, find those two points of the ecliptic in the circle of signs on the horizon, and exactly opposite to them, in the circle of months, you will find the days on which the longest day begins and ends. The day preceding the 21st of June is that on which the longest day begins, and the day following the 21st of June, is that on which it ends; the number of days between these days will show the length of the longest day at the given place. [See the Table of Climates.] THE CELESTIAL GLOBE. The celestial globe is intended to represent the starry heavens and their apparent motion from east to west. On it are drawn, the Ecliptic, the Equinoctial, the parallels of Latitude, the cir cles of declination, the meridians, the horizon, the two colures, the tropics, the polar circles, and all the constellations. In using this globe, the spectator is supposed to stand in the centre of it: hence the figure of all the constellations must be reversed, when they are to be referred to the heavens. PROBLEM I. To find the right ascension and declination of the Sun, or of a star. Bring the Sun, or star, to the brass meridian; the degrees on the Equinoctial, between the brass meridian and the first point of Aries, is the right ascension; and the degree on the brass meridian is the declination. PROBLEM II. To find the Latitude and Longitude of a star. Bring the centre of the quadrant of altitude on either pole of the Ecliptic; move the other end, till the star is at the gra How can the right ascension or declination of the Sun, or a star, be found? How can the Latitude or Longitude of a star be known? |