CHAPTER XII.

194. What is sound? What relation has sound to rapidity of vibration? Mention cases in which the vibration of sounding bodies is manifest to the sight and touch. What is said of wind instruments?

195. State the analogy of a sounding body to a pendulum. Describe the process by which the sensation of sound is produced. Where does the vibration caused by the sounding body stop in the ear? What is transmitted from thence to the brain?

196. Give examples of the transmission of sound through various substances? State the experiment by which it is shown that sound is not transmitted through a vacuum. What is said of sound at great heights?

197. How far has the sound of a volcano been heard? If the same sound were made in space at that distance from the earth why could not the inhabitants hear it? What is the cause of the noise of bodies passing through the air? Why do the heavenly bodies, moving so rapidly, produce no sound? Cite examples showing the different velocities of sound in different media.

198. What is said of the uniformity of the velocity of sound? Show how we can measure distances by sound as compared with light in velocity. Upon what does the loudness of sound depend? Illustrate this point.

199. What is said of the diffusion of sound? What of its reflection? What of echoes?

200. What is said of multiplied and mingled reflections of sound? Explain the operation of whispering galleries by Fig. 187.

201. Explain the operation of the speaking-trumpet. Give other examples of the concentration of sonorous vibrations.

202. What is the difference between a musical sound and a noise? What is said of the exact regularity of musical vibrations? How are different notes produced in stringed instruments? Upon what does the note depend in wind-instruments?

203. Explain the operation of the organ-pipe represented in Fig. 190. What is said of the notes of bells and of musical glasses? Explain the mechanism of the human voice.

204. What is harmony? Upon what does it depend? Between what two notes of the scale is there the greatest harmony? What note next to the octave harmonizes best with the fundamental note? And what note next? Show why the second note, in contrast with the octave, is so discordant with the fundamental note.

205. State the proportions between the numbers of the vibrations in the different notes. If you know the number of vibrations of the fundamental note in a second, how may you determine the number of vibrations in the other notes? What is said of the number of notes in the diatonic scale? What of the proportionate lengths of strings for different notes? What is said of tuning instruments?

206. What is meant by saying that a note is too sharp or too flat? State in full what is said about the mysteries of sound and hearing.