Part 47

43. (Pg. 98) To what use has this property of the pendulum been applied?

44. (Pg. 99) What change must be made in pendulums situated at the equator and at the poles, to render their vibrations equal?

45. (Pg. 99) What do the vibrations of a pendulum resemble, and why will it vibrate more rapidly if shortened?

46. (Pg. 99) In the revolution of the earth round the sun, what is the position of its axis?

47. (Pg. 99) How much is the axis of the earth inclined, and with what line does it form this angle?

48. (Pg. 99) What is represented by fig. 2, plate 9?

49. (Pg. 100) How is the north pole inclined in the middle of our summer, and what effect has this on the north frigid zone?

50. (Pg. 100) In what direction does the north pole always point?

51. (Pg. 100) What is shown by the position of the earth at B, in the figure?

52. (Pg. 100) How does the sun then shine at the poles, and what is the effect on the days and nights?

53. (Pg. 101) When the earth has passed the autumnal equinox, what changes take place at the poles, and also in the whole northern and southern hemispheres?

54. (Pg. 101) Why is the heat greatest within the torrid zone?

55. (Pg. 101) How does the sun appear at the poles, during the period of day there?

56. (Pg. 101) In what will the days and nights differ in the temperate zone, from those at the poles, and at the equator?

57. (Pg. 102) Trace the earth from the winter solstice to the vernal equinox, and inform me what changes take place.

58. (Pg. 102) What takes place at the time of the vernal equinox, and what is meant by the term?

59. (Pg. 102) In proceeding from the vernal equinox to the summer solstice, what changes take place?

60. (Pg. 103) From what cause arises the superior heat of the equatorial regions?

61. (Pg. 103) Why should oblique rays afford less heat than those which are perpendicular?

62. (Pg. 103) How is this explained by fig. 1. plate 10?

63. (Pg. 103) How do you account for the superior heat of summer, and how is this exemplified in fig. 2 and 3, plate 10?

64. (Pg. 104) What other cause lessens the intensity of oblique rays?

65. (Pg. 104) How is this explained by fig. 4?

66. (Pg. 104) What causes conspire to lessen the solar heat in the morning and evening?

67. (Pg. 104) The greatest heat of summer is after the solstice, and the greatest heat of the day, after 12 o'clock, although the sun's rays are then most direct, how is this accounted for?

68. (Pg. 105) Is there any change of seasons in the other planets?

69. (Pg. 105) What is said respecting the axes of Jupiter, of Mars, and of Saturn?

70. (Pg. 105) In 365 days, how many times does the earth revolve on its axis?