6. (Pg. 147) How are the trade-winds produced, and how far do they extend?

7. (Pg. 147) How is the equilibrium in the air restored?

8. (Pg. 148) How can contrary currents of air be shown in a room?

9. (Pg. 148) What causes this?

10. (Pg. 148) What is meant by a periodical wind?

11. (Pg. 148) What occasions the land and sea breezes, and where do they prevail?

12. (Pg. 149) What are monsoons?

13. (Pg. 149) How do they change, and what is the cause?

14. (Pg. 149) What is meant by their breaking up, and what effect is in general produced?

15. (Pg. 149) Why is the wind most variable in high lat.i.tudes?

16. (Pg. 150) Why is the wind apt to lessen about sunset?

17. (Pg. 150) What effect must the sun and moon produce upon the atmosphere, from their attraction?

18. (Pg. 150) Why do not the aerial tides affect the barometer?

19. (Pg. 151) How is sound produced?

20. (Pg. 151) Does sound exist in the sonorous body, if not, what is it?

21. (Pg. 151) By what experiment might we prove that air is the princ.i.p.al vehicle of sound?

22. (Pg. 152) What other bodies convey sound, and how can it be shown that they do so?

23. (Pg. 152) What is meant by a sonorous body?

24. (Pg. 152) To what do they owe this property?

25. (Pg. 152) How is this explained by fig. 6, plate 14?

26. (Pg. 152) How is it ill.u.s.trated by a stone thrown into water, and how far does this ill.u.s.tration apply?

27. (Pg. 153) How are the vibrations propagated?

28. (Pg. 153) How can we prove that sound, does not travel as rapidly as light?

29. (Pg. 153) At what rate is sound said to travel?

30. (Pg. 153) Is the velocity much influenced by the direction of the wind?

31. (Pg. 153) How will sound enable us to judge of the distance of objects?

32. (Pg. 154) How are echoes produced?

33. (Pg. 154) What is the operation and effect of the speaking-trumpet (fig. 7, plate 14)?

34. (Pg. 155) How is a musical tone produced?

35. (Pg. 155) What occasions discords?

36. (Pg. 155) Upon what does the acuteness or gravity of a sound depend?

37. (Pg. 155) Does the force, with which a string is struck, affect the rapidity of its vibrations?

38. (Pg. 155) How are the strings made to produce the high and low notes?

39. (Pg. 155) What is meant by harmony, or concord, and how is it produced?

40. (Pg. 156) When are strings said to be in unison?

41. (Pg. 156) How are octaves produced?

42. (Pg. 156) How are fifths produced?

43. (Pg. 156) How major and minor thirds?

44. (Pg. 156) What is meant by melody, and in what particular does it differ from harmony?

[Ill.u.s.tration: PLATE XV.]

CONVERSATION XIV.

ON OPTICS.

OF LUMINOUS, TRANSPARENT, AND OPAQUE BODIES. OF THE RADIATION OF LIGHT.

OF SHADOWS. OF THE REFLECTION OF LIGHT. OPAQUE BODIES SEEN ONLY BY REFLECTED LIGHT. VISION EXPLAINED. CAMERA OBSCURA. IMAGE OF OBJECTS ON THE RETINA.

CAROLINE.

I long to begin our lesson to-day, Mrs. B., for I expect that it will be very entertaining.

_Mrs. B._ _Optics is that branch of philosophy, which treats of the nature and properties of light._ It is certainly one of the most interesting branches of Natural Philosophy, but not one of the easiest to understand; I must, therefore, beg that you will give me your undivided attention.

I shall first inquire, whether you comprehend the meaning of a _luminous body_, an _opaque body_, and a _transparent body_.

_Caroline._ A luminous body is one that shines; an opaque....