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?