There are other tones, which, though they cannot be struck together without producing discord, if struck successively, give us that succession of pleasing sounds, which is called melody. Harmony, you perceive, arises from the combined effect of two, or more concordant sounds, while melody, is the result of certain simple sounds, which succeed each other. Upon these general principles, the science of music is founded; but, I am not sufficiently acquainted with it, to enter into it any further. We shall now, therefore, take leave of the subject of sound; and, at our next interview, enter upon that of optics, in which we shall consider the nature of light, vision, and colours. Questions 1. (Pg. 146) What is wind, and how is it generally produced? 2. (Pg. 146) How do the winds blow, around the place where the air becomes rarefied? 3. (Pg. 146) What effect is likely to be produced where the winds meet? 4. (Pg. 147) In what part of the globe is the air most rarefied, and what is the consequence? 5. (Pg. 147) How do these winds change their direction as they approach the equator? 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 latitudes? 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 ærial 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 principal 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 illustrated by a stone thrown into water, and how far does this illustration 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)?