70. How many days of the year does the sun rise and set alternately every twenty-four hours, at Sabine island, in the Polar Sea?

71. How do you find in what degree of north latitude, on any day between the 20th of March and 21st of June, the sun begins to shine constantly without setting, and also in what latitude in the opposite hemisphere he begins to be totally absent?

72. In what latitude north does the sun begin to shine constantly without setting, and also in what latitude south does he begin to be totally absent, on the 25th of May?

73. Given any number of days not exceeding 187 north, or 178 in south latitude, how do you find the parallel of latitude in which the sun does not set during that time?

74. In what degree of latitude north does the sun continue above the horizon during 120 days of twenty-four hours each ?

75. How do you find in what geographical climate any given place is situated?

76. In what climate is Havana?

77. How do you find the breadths of the several climates, from the equator to the poles ?

78. What is the beginning, end, and breadth of the eleventh north climate; and what remarkable places are situated within it?

79. How do you find the beginning, end, and duration of morning and evening twilight, at a given place, on a given day?

80. What is the duration of twilight at the tropic of Capricorn, on the 21st of June ?

81. How do you find the beginning, end, and duration of constant twilight at any place between the fortyninth degree of north or south latitude, and the north or south pole ?

82. What is the duration of constant twilight at Archangel?

83. Having given the place and day of the month, how do you find the sun's meridian altitude?

84. What is the sun's meridian altitude at the north polar circle, on the 22d of December?

85. The sun's meridian altitude and day of the month being given, how do you find the latitude of the place of observation?

86. On the 20th of November, 1825, the sun's meridian altitude was observed to be 40° south of the observer, what was the latitude of the place?

87. How do you find the sun's azimuth and his altitude at any given place, the day and hour being given? 88. What is the sun's altitude, and his azimuth from the north, at New-Orleans, on the 21st of June, at 9 o'clock in the morning?

89. How do you find the sun's amplitude, at a given place, the day and hour being given? 90. On what point of the compass does the sun rise and set at Albany, on the 20th of March?

91. The sun's amplitude and day of the month being given, how do you find the latitude of the place of

observation?

92. The sun's amplitude was observed to be 320 from the east towards the north, on the 21st of June; required the latitude of the place of observation.

93. How do you find the altitude of the sun at any place in the frigid zones, when it is midnight at a particular place in the torrid or temperate zones ?

94. What is the sun's altitude at Sabine Island, when it is midnight at Bejapoor, a city in Hindoostan, on the 21st of June?

95. How do you find the sun's right ascension, &c. the day of the month at any place being gwen?

96. Required the sun's right ascensior c. at Paris, on the 22d of December?

97. The day and hour at any place being given, to find all those places of the earth where the sun is rising, setting, noon, vertical, &c.

98. When it is eight o'clock in the afternoon a Rome, on the 25th of March, where is the sun rising, setting, noon, vertical, &c.?

Definitions and terms belonging to the celestial glove

1. The celestial globe, as has already been oberved, is an artificial representation of the heavens, having all the stars of the first and second magnitude, and the most noted of the rest that are visible, truly represented on it, according to their proper angular distances in the concave surface of the heavens.

2. The rotation of this globe upon its axis from east to west, represents the apparent diurnal motion of the concave surface of the celestial sphere, on an axis passing through the poles of the world, completing its revolution in 23 hours, 56 minutes, and 4 seconds nearly, and carrying along with it the sun, moon, and stars. The axis of the celestial sphere, is usually called the axis of the heavens.

This hypothesis illustrates and represents the apparent diurnal motion of the several celestial objects in parallel circles, with an equable motion, each completing its circular path in the same time. That the motion of each star is equable, and that they describe parallel circles on the concave surface, we reduce from observation and the computa tion of spherical trigonometry.-See Dr. Brinkley's Astronomy.

3. The wooden horizon circumscribing the ce lestial globe, is divided exactly into the sam

concentric circles, as the wooden horizon of the terrestrial globe. See Book I. Chap. IV.

The horizon of the celestial globe must be considered as continued to pass through the centre, where the eye is supposed situate viewing the hemisphere above the horizon, and the axis of the globe is to be placed at the same elevation as the axis of the concave surface of the spectator. In this way all the circles of the celestial sphere will be easily understood. Any consideration of the form or figure of the earth is entirely foreign to a knowledge of the circles of the sphere. They were originally invented without any reference to it. And in fact, the progress in astronomy was from the celestial circles to terrestrial, and not the contrary.

4. That imaginary great circle in the heavens, which the sun describes in his apparent diurnal revolution at the time of the equinoxes, or when the days and nights are equal all over the world, is called the equinoctial, and sometimes the celestial

equator.

The circle in which the plane of the equinoctial cuts the surface of the earth, is usually called the equator or terrestrial equator, which has been already defined, (Art. 5, page 8.)

It is however proper to observe, that in treatises on astronomy and the globes, the terms equinoctial and equator are used indifferently for each other.

5. A great circle passing through the poles of the world and through the zenith of a place, is called the celestial meridian of that place. The celestial meridians are also called circles of declination. (See Art. 5, page 21.)

The circle in which the plane of the celestial meridian intersects the surface of the earth, is called the terrestrial meridian. Those terms are used indifferently for each other. (See Art. 10, page 9.)

There are no meridians drawn on the celestial globe; but they are supplied by the brazen meridian, which is graduated in the same manner as the brazen meridian belonging to the terrestrial globe. (Art. 12, page 10.)