A Philosophical Essay of Musick

Now, if the air that is moved by being enclosed maintains such a degree of resistance to compression that it has a "spring" The author refers to the elasticity or "springiness" of air, a concept pioneered by Robert Boyle. vibrating at the same frequency as the sound that puts it into motion, the same effect will occur as when two strings are tuned in unison. That is, the motion will be so increased by succeeding regular pulses that the enclosed air may be brought to ring and produce a tone.

Vitruvius Marcus Vitruvius Pollio, a Roman architect and engineer of the 1st century BC. in his Architecture advises that in building a theater, there should be vases or hollow pots of several sizes—to correspond to all the notes of music—placed upon the stage in such a manner that the voices of those who sang upon the stage might be increased by the ringing of the vessels. He mentions various ancient theaters where such vessels existed, some made of brass and some of earthenware.

An organ pipe of a very deep bass will not sound original: "speak" suddenly when it is played alone; but if an octave is played at the same time, it will respond to the quickest touch. This is because the tone of the smaller pipe, being in harmony, causes a motion of the air included in the larger pipe. The vibrations of the included air, being coincident with those of the tone of the pipe, promote its sounding by putting the pulses at the mouth into a regular motion, or at least assisting in doing so.

These instances show the manifest effects of sound. Certainly, sounds in discord are in opposition and offer violence to one another; but sounds in musical chords are consistent, united together, and promote each other, as I have previously shown in my discussion concerning the relation of tones.

The synchronous motion of the pulses at the mouth of the pipe with the vibrations of the included air promotes the sound of the pipe, and it is difficult for a pipe to sound where those motions are in opposition. However, if by strengthening the blast of air, the pulses at the mouth are so quickened that they maintain a musical proportion to the vibration of the enclosed air—such as 2 to 1, 3 to 2, 4 to 3, 5 to 4, etc.—there will be no hindrance, but rather some advantage. Thus, it may be easily imagined