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QUESTIONS.

These are the questions which the author has used in his own classes for review and examination. In the historical portion, he has required his pupils to write articles upon the character and life of the various persons named, gathering materials from every attainable source. He has also introduced whatever problems the class could master, taking topics from the article on Celestial Measurements and the various mathematical treatises.

Introduction.—Define Astronomy. Is the earth a planet? What is the difference in the appearance of a fixed star and a planet? What is the Milky Way ?—HISTORY. What can you say of the antiquity of astronomy? How far back do the Chinese records extend? Name some astronomical phenomena they contain.

17. Why should the Chaldeans have become versed in this study? How ancient are their records? What discoveries did they make? What Grecian philosopher early acquired a reputation in this science? What other discovery did Thales make (Phil., p. 261)? What did he teach? What memorable eclipse did he predict? What were the names of two of his pupils? What did Anaximander teach?

18. Anaxagoras? What was his fate? In what century did Pythagoras live? What was his characteristic trait? Did he have any proof of his system? Explain his theory. How does it differ from ours? What strange views did he hold? What theory did Eudoxus advance?

19. What is the theory of the crystalline spheres? What has Hipparchus been styled? What addition did he make to astronomical knowledge? How many stars in our present catalogue (p. 228)? How did Egypt rank in science at an early day? What preparation did the Grecian philosophers make to fit themselves for teachers? How long did Pythagoras travel for this purpose? What can you say of the school at Alexandria? What great work did Ptolemy write there? What theory did he expound?

20. Was it original? What discovery did Eratosthenes make? Describe that method (p. 309). Show how the movements of the planets puzzled the ancients. What was the theory of "cycles and epicycles?"

21. Did the ancients believe in the reality of this cumbrous machinery? Did this theory possess any accuracy? Could they adapt it to explain any new motion?

22. What was the remark of Alphonso? When did astronomy cease to be cultivated as a science? In what century? Why did Caesar import an astronomer? Why did he attpmpt to revise the Calendar? What change did he make (p. 295)? State something of the repute in which astrology was held.

23. Tell what you can of the system. What use did it subserve? What theory displaced the Ptolemaic? When? Was the system of Copernicus original? What credit is due him? Describe his idea of apparent motion. How did he apply this to the heavenly bodies?

24. What crudity did he retain? Who was Tycho Brahe? What was his theory? How did it differ from Ptolemy's and Copernicus's?

25. What good did he accomplish? Could he generalize his facts? Had he a telescope? How did Kepler differ from Brahe? What were the two prominent characteristics of Kepler? Give his three laws. Tell how he discovered the first. The second. The third (p. 313). Describe the ellipse. Define focus, perihelion, and aphelion. What remarkable statement did Kepler make?

29. When did Galileo live? What discoveries did he make in Natural Philosophy? In Astronomy? What advantage did he have over his predecessors?

30. Give an account of his observations on the moon. On Jupiter's moons.

31. Why did this settle the controversy between the Ptolemaic and the Copernican system? How were Galileo's discoveries received!? Give some of Sizzi's ponderous arguments.

33. Who discovered the law of gravitation? Repeat it. How was this idea suggested? What familiar laws of motion aided Newton? How did he apply these to the motion of the moon? Repeat the story of his patient triumph.

35. What is the celestial sphere? Give the two illustrations which show its vast distance from the earth.

36. Why can we not see the stars by day, as by night? What portion of the sphere is visible to us? Name the three systems of circles.

37-41. Name and define (1) the principal circle, (2) the secondary circles, (3) the points, and (4) the measurements of each system. Define, especially, because in common use, zenith, nadir, azimuth, altitude, equinoctial, right ascension, declination, equinox, ecliptic, colure, and solstice. What is N or S in the heavens? What is the Zodiac?

42. How wide? How ancient? How divided? Give the names and signs. State the meaning of each (p. 229).

II. The Solar System.

Of what is the solar system composed? Describe how we are to picture it to ourselves.

The Sun.—Its sign. Its distance from us? Illustrate.

47. How are celestial distances measured? To what is the sun's light equal? To how many full moons? Its heat? Illustrate. What proportion of the sun's heat reaches the earth?

48-50. Its apparent size? How does this vary? Its dimensions—(i) diameter—illustrate, (2) volume, (3) mass, (4) weight, (5) density. How large did Pythagoras think the sun is? Tell something about the force of gravity in the sun. How much would you weigh if carried to its surface? (This can be calculated from the table in Appendix.) How does the sun appear to the naked eye? How can we see the spots? What were formerly the views of astronomers with regard to the sun's face? When were the spots discovered?

52. Tell something about the number of the spots. Their location. Size.

53. Describe the parts of which they are composed. The motion of the spots.

54-5. How do they change in form as they pass across the disk? What does this prove? What is the length of a solar axial revolution? Explain a sidereal and a synodic revolution.

56-7. Why do not the spots move in straight lines? Show how they curve. Tell what you can about the irregular movements of the spots. Tell how suddenly they change.

58. What can you say about their periodicity? Who discovered this? Is there any connection between the solar spots and the aurora? Tell the influence of the planets on the spots. Explain.

59. Do the spots affect the fruitfulness of the season? Docs the temperature of the spots differ from that of the rest of the sun? Are they depressions in the sun? How much darker are they than the adjacent surface?

60. Is the sun brighter than the Drurnmond light? Ans. The sun gives out as much light as one hundred and forty-six lime-lights would do, if each were as large as the sun and were burning all over. What are the facuke? Describe the mottled appearance of the sun.

61. What is the shape of the bright masses? What is a pore?

62. Describe the constitution of the sun according to Wilson's theory. How are the spots produced? The facula??

63. The penumbra? The umbra?

64. What is Kirchhoff s theory? How are the spots produced? The umbra? The penumbra? Upon what does this theory depend (p. 286)? What is the cause of the heat of the sun? Will the heat ever cease ? *

The PLANETS.—Name the six characteristics common to all the planets.

67. Compare the two groups of the major planets.

68. Draw an ellipse, and name the various parts. Define the ecliptic, f The ascending node. The descending node. Line of the nodes. Longitude of the node. Tell what you can with regard to the comparative size of the planets. ,

71. What is a conjunction? Name the earliest that are recorded.

72. Tell what you can concerning the planets being inhabited.

74. What about the conditions of life on the different planets? What are the two divisions of the planets?

75. What causes the apparently irregular movements of the planets? Define heliocentric and geocentric place. Illustrate. In what part of the sky is an inferior planet always seen? Define inferior and superior conjunction.

76. Greatest elongation. Quadrature. Why is a star at one time "evening" and at another "morning star?"

77. What is a transit? Explain the retrograde motion of an inferior planet. (This motion, it will be remembered, was one that sorely puzzled the ancients.)

*If we accept the Nebular hypothesis (p. 283), we must suppose that the heat is produced by the condensation of the nebulous matter and consequent chemical changes. The sun is radiating its heat constantly, and, after a time, will go out, in turn, as the earth and all the planets have before it.

fLockyer beautifully says: "We may imagine the earth floating around the sun on a boundless ocean, both sun and earth being half immersed in it. This level, this plane, the plane of the ecliptic (because all eclipses occur in it), is used by astronomers as we use the sea-level. We say a mountain is so far above the level of the sea. The astronomer says a star is so high above the level of the ecliptic."

78. Describe the phases of an inferior planet. Why does an inferior planet have phases? Define gibbous.

79. Explain the opposition and conjunction of a superior planet. Its retrograde motion. Must a superior planet always be seen in the same part of the sky as the sun?

80. Which retrogrades more, a near or a distant planet? Define a sidereal and a synodic revolution of an inferior and a superior planet, and tell what you can about each. In what case would there be no difference between a sidereal and a synodic revolution? Why is a planet invisible when in conjunction? ,

82. When is a planet evening, and when morning star? Tell what you can about the supposed discovery of a planet interior to Mercury.

83. Mercury.—Definition and sign? Describe the appearance of Mercury, and where seen.

84. What was the opinion of the ancients? The astrologists? Chemists? Why is it difficult to see it? When can we see it best?

85. What is the peculiarity of its orbit? Its distance from the sun? Velocity? Length of its day? Year? Difference between its sidereal and synodic revolution? why? Its dis tance from the earth?

86. Show why its greatest and least distances vary so much. What is its diameter? Volume? Density? Force of gravity? Specific gravity? How much would you weigh on Mercury? Describe its seasons. (If the pupil does not understand pretty well the subject of the terrestrial seasons, it would be well here to read carefully page no, et seq.)

88. Its temperature? Appearance of the sun? Has it any moon? What is the appearance of the planet through a telescope? What do these phases prove? What do we know of its mountains and valleys?

89. Venus.—Definition and sign? Ancient names? Appearance to us?

90. When brightest? Can Venus be seen by day? Illustrate.

91. Describe the orbit. What is the distance of Venus from the sun? Velocity? Length of the year? Day? Difference between the sidereal and synodic revolution? Distance from the earth?

92. How does the apparent size vary? When is Venus the brightest? What is the diameter? Volume? Density?

93. Force of gravity? Does the force of gravity increase

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