ent bearings of places with perfect accuracy, which cannot be done on any other map. 38. Plain charts have the meridians, as well as the parallels of latitude drawn parallel to each other, and the degrees of latitude and longitude equal to those at the equator. 39. The armillary sphere is an astronomical instrument, representing the several circles of the sphere in their natural order, serving to give an idea of the office and position of each of them. It is thus called, as consisting of a number of circles or rings, which were called by the Latins, armillæ, from their resembling bracelets, or rings. made for the arm.-[Fig. 7.] Definitions of Terms necessary to be understood in the solution of Problems on the Terrestrial and Celestial Globes. 40. The terrestrial globe is an artificial representation of the earth. In the figure 1, the globe is represented out of its stand, that the differentcircles, &c. may be distinctly seen. 41. The grand divisions, different empires, kingdoms, countries, chief cities, oceans, seas, rivers, &c. are represented on the terrestrial globe, according to their relative situations on the real globe of the earth. 42. The diurnal motion of the terrestrial globe is from west to east. 43. The axis of the earth is an imaginary line passing through the centre of it, on which it is supposed to turn, and about which all the heavenly bodies appear to have a diurnal revolution. 44. The axis of the earth is represented by the wire which passes from north to south, through the middle of the artificial globe.-[Fig. 1.] 45. The poles of the earth are the two extremities of its axis; one of which is called the north or arctic; the other, the south or antarctic pole.-[Fig. 1.] 46. The celestial poles are two imaginary points in the heavens, exactly above the terrestrial poles. Or, if the axis of the earth were prolonged until it came in contact with the starry heavens, it would touch the celestial poles in two points, one of which, would be within two degrees of the pole star,* in the end of the tail of the Little Bear. 47. The brazen meridian is the circle in which the artificial globe turns, and is divided into 360 equal parts, called degrees.-[Fig. 1.] 48. Every circle is supposed to be divided into 360 degrees; each degree into 60 minutes, and each minute into 60 seconds. 49. A degree of a great circle in the heavens is a space nearly equal to twice the apparent diameter of the sun, or to twice that of the moon, when considerably elevated above the horizon.. 50. The degrees in the upper semi-circle of the brazen meridian, are numbered from 0 to 90 from the equator towards the poles, and are used for finding the latitudes of places. 51. On the lower semi-circle of the brazen meridian, the degrees are numbered from 0 to 90, from the poles towards the equator, and are used in the elevation of the poles. 52. Great circles divide the globe into two equal parts, as the equator, the ecliptic, the rational horizon, and the brazen meridian, when assumed * The pole star, is a star of the second magnitude, near the north pole, in the end of the tail of the Little Bear. Its mean right ascension, for the beginning of the year 1804, was 13° 14′ 43′′ and its declination 88° 14' north. Mr. Bowditch gives its right ascension in time 52′ 15′′, for 1800, as the meridian of any particular place; and the colures on the celestial globe.* 53. The equator is a great circle of the earth, equidistant from the poles, and divides the globe into two hemispheres, northern and southern.[Fig. 1.] 54. The latitudes of places are counted northward and southward from the equator; and the longitudes of places are reckoned upon it eastward and westward. 55. The equator when referred to the heavens, is called the equinoctial, because when the sun appears in it, the days and nights are equal all over the earth, viz. 12 hours each. 56. The first meridian, is that from which geographers begin to count the longitude of places. In English maps and globes, the first meridian is a semi-circle supposed to pass through London or the royal observatory of Greenwich. 57. Meridians, or lines of longitude, are semicircles, extending from the north to the south pole, and cutting the equator at right angles.[Fig. 2.] 58. Every place on the globe, is supposed to have a meridian passing through it, though there are 24 only drawn on the artificial globe; the deficiency is supplied by the brass meridian. 59. When the sun comes to the meridian of any place (not within the polar circles,) it is there noon or mid-day. 60. When the brass meridian stands over any particular place, representing its meridian, it is considered as a great circle, dividing the globe into the eastern and western hemispheres.-[Fig. 1.7 61. The ecliptic is a great circle in which the sun makes his apparent annual progress among * Secondaries to a great circle are great circles which pass through its poles, and consequently must be perpendicular to it. the fixed stars; or it describes the real path of the earth round the sun, and cuts the equator, when drawn on the terrestrial globe, in an angle of 23° 28'. The points of intersection are called the equinoctial points. [Fig. 2.] 62. Small circles divide the globe into two unequal parts. 63. The tropics are two small circles parallel to the equator at the distance of 23° 28′ from it; the northern, is called the tropic of cancer, and the southern, the tropic of capricorn.-[Fig. 2.] 64. The tropics are the limits of the torrid zone. 65. The polar circles are small circles parallel to the equator, at the distance of 66° 32′ from it, or 23° 28′ from each pole. The northern is called the arctic; the southern, the antarctic circle. [Fig. 2.] 66. Parallels of latitude are small circles drawn through every ten degrees of latitude, on the terrestrial globe, parallel to the equator.-[Fig. 2.] 67. Every place on the globe is supposed to have a parallel of latitude drawn through it, though there are, in general, only sixteen parallels drawn on the terrestrial globe. 68. The hour circle on artificial globes, is a small circle of brass, with an index fixed to the north pole. This circle is divided into twentyfour equal parts, correspondent to the hours of the day; and these again are subdivided inte halves and quarters. 69. The equator is also an hour circle, being on the best globes so divided by meridian lines, drawn through every fifteen degrees of longitude, as to answer every purpose to which the brass circle can be well applied. 70. The ecliptic is divided into twelve equal parts, called signs, each containing thirty degrees. The sun makes his apparent annual progress. through the ecliptic, at the rate of nearly one degree in a day.-[Fig. 2.] L 71. The names of the signs and their characters, and the days on which the sun enters them, are as follow: Vernal Signs. Aries, the ram,-21st of March. Cancer, the crab,-21st of June. mg Virgo, the virgin,-22d of August. Libra, the balance, 23d of September. m Scorpio, the Scorpion,-23d of October. ↑ Sagittarius, the archer,-22d of November.. Winter Signs. Capricornus, the goat,-21st of December. Aquarius, the water-bearer,-20th of January. * Pisces, the fishes,-19th of February. 72. The vernal and summer signs are called northern signs; because when the sun is in any of them, his declination is north. 73. The autumnal and winter signs are called southern signs; because when the sun is in any of them, his declination is south. 74. The vernal and autumnal signs are called ascending signs; because when the sun is in any of them, his declination is increasing. The summer and winter signs, are called descending signs; because when the sun is in any of them, his declination is decreasing. 75. Declination of the sun, a star, or planet, is its distance from the equinoctial, northward or southward. 76. When the sun is in the equinoctial he has no declination, and enlightens half the globe from pole to pole. As he increases in north declina |