8. (Pg. 92) What is meant by a plane, and how could one be represented?

9. (Pg. 93) Describe what is intended by the plane of the earth's...o...b..t.

10. (Pg. 93) Extending this plane to the fixed stars, what circle would it form, and among what particular stars would it be found?

11. (Pg. 93) What is fig. 1. plate 9, designed to represent?

12. (Pg. 93) The ecliptic does not properly belong to the earth, for what purpose then is it described on the terrestrial globe?

13. (Pg. 93) What does the obliquity of the ecliptic to the equator serve to show?

14. (Pg. 93) Within what limits do you find the torrid zone?

15. (Pg. 93) What two zones are there between the torrid, and the two frigid zones?

16. (Pg. 93) Where are the frigid zones situated?

17. (Pg. 93) What is meant by the term zone; and are the frigid zones properly so called?

18. (Pg. 93) How do meridian lines extend, and what is meant by the meridian of a place?

19. (Pg. 93) What is said of the meridian to which the sun is opposite, and where is it then midnight?

20. (Pg. 94) What hour is it then, at places exactly half way between these meridians?

21. (Pg. 94) How are greater and lesser circles distinguished?

22. (Pg. 94) What part of a circle is a degree, and how are these further divided?

23. (Pg. 94) What is the diameter, and what the circ.u.mference of a circle, and what proportion do they bear to each other?

24. (Pg. 94) What part of a circle is a meridian?

25. (Pg. 94) How many degrees are there between the equator and the poles?

26. (Pg. 94) Into what parts, besides degrees, is the ecliptic divided?

27. (Pg. 94) How are degrees of lat.i.tude measured, and to what number do they extend?

28. (Pg. 94) On what circles are degrees of longitude measured, and to what number do they extend?

29. (Pg. 94) What is a parallel of lat.i.tude?

30. (Pg. 95) Degrees of longitude vary in length; what is the cause of this?

31. (Pg. 95) What is the length of a degree of lat.i.tude, and why do not these vary?

32. (Pg. 95) What causes the equator to be somewhat larger than a great circle pa.s.sing through the poles, and what effect has this on degrees of longitude measured on the equator?

33. (Pg. 95) What is the cause of this form being given to the earth?

34. (Pg. 96) What would have been a consequence of the centrifugal force, had the earth been a perfect sphere?

35. (Pg. 96) A body situated at the poles, is attracted more forcibly than if placed at the equator, what is the reason?

36. (Pg. 97) What effect would be produced upon the gravity of a body, were it placed beneath the surface of the earth, and what supposing it at its centre?

37. (Pg. 97) What two circ.u.mstances combine, to lessen the weight of a body on the equator?

38. (Pg. 97) Why could not this be proved by weighing a body at the poles, and at the equator?

39. (Pg. 98) What is a pendulum?

40. (Pg. 98) What causes it to vibrate?

41. (Pg. 98) Why are not its vibrations perpetual?

42. (Pg. 98) Two pendulums of the same length, will not, in different lat.i.tudes, perform their vibrations in equal times, what is the cause of this?

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 pa.s.sed 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.