378 Dynamic Theory. 



and their varying proportional force. Almost all musical sounds are 

 the resultants of such mixture of fundamental and harmonic tones, and 

 very few musical bodies are free from the harmonics. But it is possi- 

 ble to construct such instruments, and Helmholtz has furnished them in 

 what he calls the resonators. They consist each of a hollow metallic 

 globe with a large open neck at one end and a small one at the other. 

 They are constructed of various sizes and each one has only its funda- 

 mental tone without harmonics. Whenever the fundamental note of one 

 of these resonators is sounded by another instrument the air contained 

 in it is set to vibrating and thus reinforcing the sound, but it is silent 

 unless its particular note is started. With these instruments the dif- 

 ferent, simple or pure sounds that go to make a composite note can each 

 be picked out. It is in this way that the harmonics and accompanying 

 sounds that go along with almost every fundamental tone have been 

 sorted out and identified. We cannot fail to note in all phenomena of 

 sound the paramount influence of the form and constitution of the 

 mediums through which it is propagated. These mediums have noth- 

 ing to do with the origination of the energy which finally is resolved 

 into the sensation of sound. But they happen in its way and are acted 

 upon by it, made to vibrate and to communicate their vibrations to 

 the air. As energy acting on machinery of different forms and adjust- 

 ments furnishes a variety of modes of molar motion, so when the 

 molar motion is reduced to molecular vibration the form and adjust- 

 ment of the body moved is all-important in determining the kind of 

 motion developed in it, the period of the vibration, the length and 

 amplitude of the waves, the number and pitch of the harmonics and 

 the accompanying clangs and noises, or whether the vibratory movement 

 results in any such phenomenon as sound at all. But no body whatever 

 its form can escape being affected in some way whenever it is reached 

 by the aerial vibrations. A molecular change of greater or less impor- 

 tance is inevitably accomplished, and if the body is a sonorous body these 

 vibrations may pass on through it, exciting its fundamental tone on the 

 way, and be again delivered to the air for further propagation. If the 

 body impinged upon be an organized body the molecular vibration set 

 up in it may be quenched in giving rise to sensation, that is, disappear- 

 ing as one mode of molecular vibration it reappears as another. It can- 

 not disappear from the domain of physics, nor be lost as physical energy. 

 And it follows that if it does really disappear in giving rise to a sensa- 

 tion in an organism, that sensation is a form of physical energy. This 

 important point is to be discussed further on. 



It has been observed that sound is a vibration in ponderable matter. 

 Accordingly we find that sound is not transmitted through a vacuum. A 

 bell suspended by a string and rung in a receiver exhausted of air can- 



