"Unquestionably, any animal, by patience, will learn the meaning of sounds. Constant repetition of certain notes causes birds to repeat them. I have known dogs to perform almost anything they were told to do, although they are not able to utter a single sound of the words emitted in giving the command."
"Well, what is it that causes sound?"
"The most wonderful thing in nature is, that she manifests herself in only one way, namely, by a movement, or a motion of some kind. Vibration is the term used to designate this. Sound, light, heat, taste, smell, and everything which becomes sensible to us is produced by vibration. The movements of the heavenly bodies, swinging back and forth around the sun, like huge pendulums, the movement of the sap in trees, up and down, the beating of the heart, the winking eyelids are all motions which show energy, development, life."
"But what is it that makes us understand one sound from the others?"
"Simply the difference in the kind of vibration. There are three things which characterize sounds; namely, pitch, intensity and character. Pitch depends on the rapidity of the vibrations; intensity on the extent or the amplitude of the vibrations; and character on the substance or instrument producing them. To illustrate: When you sing a very high note the vibrations may be five thousand vibrations a second, or there may be only two thousand during that time. That represents the pitch. In singing that note you may sing it so loud that, like a pendulum, it will swing way over to one side, or it may move only a short distance. That represents intensity. If either you or George had sung that note I should have been able to detect it, whatever its pitch or intensity, because your voices are as unlike as different musical instruments, and that is character, or timbre, as the French call it."
CHAPTER III
THE HIDDEN MESSAGE
While the work of getting out the planking for the boat was going on, and the plowing had now been resumed, since the new yoke of oxen were fitted to do the work, the boys were not forgetful of the usual weekly outing. They had several quite important things right at home which needed looking into, if they wanted to solve some of the things on the island. First, the cave, which they had twice attempted to explore; the search for their lost boat, which had the strange rope and oars; and the mystery of the flag and pole.
These things weighed heavily on their minds, because these happenings were close at hand. But what made the greatest impression on the minds of all was the finding of the Investigator's lifeboat. It seemed almost like a call to them from the interior. The impatience of the boys was almost beyond restraint, at times.