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How can it be changed into mean time? Tell how to erect a sun-dial. When will a sidereal and a mean-time clock coincide? A mean-time clock and the sun-dial?

292. Give the two reasons why the solar days are of unequal length.

294. What is the civil day? Who invented the present division? Describe the customs of various nations. What is the origin of the names of the days ?* What is the sidereal year? The mean solar year? What causes the difference?

295. What is the anomalistic year? How did the ancients find the length of the year? What error did they make? What was the result? Give an account of the Julian calendar. The Gregorian calendar. What is the meaning of the terms O. S. and N. S.? What country now uses O. S.? When was the change adopted in England? How was it received? How could a child be eight years old before a return of its birthday?

297. When do the Jews begin their year? Why does our year begin January 1st? Show how the earth is our timepiece. What influence has Jupiter's moons on the cotton trade?

Celestial Measurements.—These problems are to be used throughout the study. They require no questions but the formal statement of the problem requiring solution.

* It is said that the Egyptians named the seven days from the seven celestial bodies then known. The order was continued by the Romans. Tuesday they called Dies Marth § Wednesday, Dies Mercurii; Thursday, Dies Jovis; Friday, Dies Veneris. In the Saxon mythology, Tius, Woden, Thor, and Friga are equivalent to Mars, Mercury, Jupiter, and Venus. Hence we see the origin of our English names.

GUIDE TO THE CONSTELLATIONS.

The following is a description of the appearance of the heavens on or about the first day of each month in the year.

January, (7 p. M.)—In the North, Cassiopeia and Perseus are above Polaris, Cepheus and Draco west, Ursa Minor below, and Ursa Major below and to the east. In the East, Cancer is just rising, Canis Minor (Procyon) has just risen. Along the Ecliptic, Gemini is well up, then Taurus, Aries reaches to the meridian, next Pisces, Aquarius (letter Y) and Capricornus just setting. In the Southeast, Orion and the Hare are well up. In the South, Cetus swims his huge bulk far to the east and west. In the Southwest is Piscis Australis (Fomalhaut). North of the Ecliptic the Triangles are nearly in the zenith, Perseus is just east, below is Auriga, Andromeda lies just west of the meridian, and Pegasus is midway, while Delphinus (the Dolphin, Job's Coffin), Aquila (Altair), and Lyra (Vega) are fast sinking to the western horizon.

February e (7 p. M.)—In the North, Ursa Major lies east of Polaris, Ursa Minor and Draco below, Cepheus west, Cassiopeia above and to the west. In the East, Regulus and Cor Hydras are just rising. Along the Ecliptic, Leo (Regulus, the sickle) just rising, Cancer well up, Gemini midway, Taurus on the meridian, Aries (the scalene triangle) past, Pisces next, and lastly Aquarius just setting. In the Southeast, Canis Minor, Canis Major (Sirius), and Orion are conspicuous. In the Southwest, Cetus covers nearly the whole sky. North of the Ecliptic, Perseus is on the meridian, while Auriga is a little east of it; west of Perseus is Andromeda, while the great square of Pegasus is fast approaching the horizon.

March. (7 p. u.)—In the North, Ursa Major lies east of Polaris, Draco and Ursa Minor below, Cepheus below and to the west, and Cassiopeia west. In the East, Cor Caroli (the Greyhound) is well up, and Coma Berenices is rising. Along the Ecliptic, Leo is fully risen, next Cancer, Gemini reaches to the meridian, Taurus is past, Aries midway, and lastly Pisces is just beginning to set. In the Southeast, Cor Hydras, Canis Minor and Canis Major are conspicuous. In the South, Orion blazes brilliantly. In the Southwest, Cetus is hiding below the horizon. North of the Ecliptic, Auriga is in the zenith; west are Perseus and Andromeda, while Pegasus is just beginning to sink out of sight.

April. (7 p. M.)—In the North, Ursa Major is above and to the east of Polaris; opposite and to the west is Perseus, Draco below and to the east, Cepheus below and to the west, Cassiopeia west. In the East, Bootes (Arcturus) not quite fully risen. Along the Ecliptic, Virgo (Spica) rising, Leo midway, Cancer reaches to the meridian, Gemini past, next Taurus, then Aries, and lastly Pisces just setting. In the Southeast is the Crater (the Cup), and Hydra stretches its long neck to the meridian. In the South, Canis Minor. In the Southwest, Sirius and Orion. North of the Ecliptic, and in the northeast, are Coma Berenices and Cor Caroli; above Gemini and Taurus is Auriga, while Andromeda is just setting in the northwest.

May. (8 P. M.)—In the North, Ursa Major is above Polaris, Ursa Minor and Draco east, Cepheus and Cassiopeia below, and Perseus west. In the East, Lyra is just rising, and Hercules is just up. Along the Ecliptic, Libra is just rising, Virgo is midway, Leo is on the meridian, Cancer is past, next Gemini, and lastly Taurus just setting. In the South, stretching east and west of the meridian, is Hydra, with the Crater and Corvus a little east. In the Southwest, is Cor Hydras, Canis Major, and Canis Minor, while Orion is just setting in the west. North of the Ecliptic, in the east, above Hercules, are Corona Borealis (The Northern Crown), Bootes (Arcturus), Coma Berenices, and Cor Caroli, which stretch nearly to the meridian. In the Northwest, above Taurus and Perseus, is Auriga.

June. (8 P. M. )-~In the North, Ursa Major is above Polaris, Draco and Ursa Minor to the east, Cepheus below and to the east, and Cassiopeia directly below. In the East, Cygnus and Aquila are just rising, Lyra and Taurus Poniatowskii are well up. Along the Ecliptic, Scorpio is rising, Libra is midway, Virgo on the meridian, Leo past, Cancer midway, Gemini next, and Taurus just setting. In the South are Corvus and the Crater, a little past the meridian. In the Southwest is Cor Hydrse, and in the west Canis Minor approaching the horizon. North of the Ecliptic, in the east, above Scorpio, is Hercules; then Corona and Bootes, and near the meridian, Cor Caroli and Coma Berenices. In the Northwest is Auriga, just coming to the horizon.

July. (9 p. M.)—In the North, Draco and Ursa Minor above Polaris, Ursa Major west, Cepheus east, and Cassiopeia below to the east. In the East, the Dolphin (Job's Coffin) is row well up, Cygnus is almost midway to the meridian, and Lyra is still higher. Along the Ecliptic, Capricornus is rising, Sagittarius (the Archer) is next, Scorpio, with its long tail swinging along the horizon, is directly south, Libra is past the meridian, Virgo midway, and Leo has almost reached the horizon. In the Southwest, the Crater is setting, and Corvas is just above. North of the Ecliptic, above Scorpio and east of the meridian, are Serpentarius, Hercules, and Taurus Poniatowskii; Corona is almost on the meridian, to the west of which lie Bootes, Cor Caroli, and Coma Berenices.

August* (9 P. M.)—In the North, Draco and Ursa Minor are above Polaris, Cepheus above and to the east, Cassiopeia east, and Ursa Major west. In the Northeast, Perseus is just rising, while south of it Andromeda and Pegasus are fairly up. Along the Ecliptic, Aquarius is risen, next Capricornus, Sagittarius reaches to the meridian, Scorpio is just past, Libra next, and Virgo (Spica) just touches the horizon. North of the Ecliptic, Taurus Poniatowskii is on and Lyra is just east of the meridian; the Swan and Dolphin are east of Lyra, Serpentarius and Hercules are above Scorpio, and just west of the meridian; thence west are Corona and Bootes, while far in the northwest are Coma Berenices and Cor Caroli.

September. (8 p. M.)—Draco is above and to the west of Polaris, Cepheus above and to the east, Cassiopeia east, Ursa Major is below and to the west. In the Northeast, Perseus is just rising. In the East, Andromeda is fairly up, Pegasus is nearly midway to the meridian. Along the Ecliptic, Pisces is just rising, next Aquarius, Capricornus in the southwest, Sagittarius on the meridian in the south, next Scorpio in the southwest, Libra, and lastly Virgo just setting. North vf'the Ecliptic, Lyra is on the meridian, Cygnus, the Dolphin, and Aquila just to the east, while to the west are Taurus Poniatowskii and Serpentarius; north of these latter are Hercules, Corona, Bootes, Cor Caroli, and Coma Berenices.

October* (7 P. M.)In the North, Cepheus and Draco are above Polaris, Ursa Minor west, Cassiopeia east, and Ursa Major below and west. In the Northeast, Perseus is fairly risen. In the East, Andromeda is nearly midway to the zenith. Along the Ecliptic, Aries is just rising, Pisces well up, Aquarius and Capricornus in the southeast, Sagittarius in the south, Scorpio far down in the southwest, and Libra just setting. North of the Ecliptic, Cygnus and Aquila are on the meridian, the Dolphin just east of it, and far south; Lyra is west of the meridian, Taurus Poniatowskii lower down and to the south, Serpentarius is just above Scorpio; next, in line with it and Polaris, is Hercules; Corona and Bootes are toward the northwest, where Coma Berenices is just setting.

November. (7 p. M.)—In the North, Ursa Major is below Polaris, Ursa Minor and Draco are to the west, Cepheus above, and Cassiopeia above and to the east. In the Northeast, Auriga is just rising, and Perseus is above, nearly midway to the meridian. Along the Ecliptic, Taurus is just rising, next Aries and Pisces; Aquarius is on the meridian, south; then Capricornus, and lastly Sagittarius, in the southwest. North of the Ecliptic, Pegasus and Andromeda lie east of the meridian, the Swan, Dolphin, Eagle, Taurus Poniatowskii, and Lyra west. In the Northwest are Hercules and Corona.

December. (7 p. M. )-—In the North, Cassiopeia is above Polaris, Cepheus above and to the west, Perseus above and to the east, Draco west, and Ursa Major below. In the Northeast, below Perseus, is Auriga. In the East, Orion is rising. Along the Ecliptic, Gemini is just rising, Taurus is nearly midway, next Aries, Pisces is on the meridian, then Aquarius, and lastly Capricornus, far in the southwest. In the South, east of the meridian, is Cetus, and west is Fomalhaut. North of the Ecliptic, Andromeda is nearly on the meridian, and Pegasus west of it; Cygnus, Delphinus, Lyra, and Aquila are about midway, while Taurus Poniatowskii is just sinking to the horizon. In the Northwest, Hercules is just setting.

Note.—It should be borne in mind that a month makes a variation of about two hours (30°) in the rise of a star: hence, in the foregoing- "Guide," the "January Sky" of 9 p. M. would be about the same as the "February Sky" of 7 p. M.; the " January Sky" of 11 p. M. would be about the same as the "March Sky" of 7 p. M., &c. In this way the "Guide" may be used for any hour in the night. The pupil will see that in the " Guide" the prominent figures and stars in each constellation are given in parentheses. Examples: the "Y" in Aquarius, the "scalene triangle" in Aries, "Job's coffin" in the Dolphin, "Procyon" in Canis Minor, &c. These aid in identifying the constellation.

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