CHAPTER ONE

§. 2. All those who have written even somewhat plausibly on this subject establish that sound consists in the air, and that the air is, as it were, its vehicle, by which it is carried in every direction from its source. Indeed, the matter cannot be otherwise, since nothing exists except air that surrounds our ears and is capable of producing a change within them. For although it might be objected that the mechanism of hearing is perhaps arranged in the same way as smell and sight—senses which are excited not by the air itself, but by actual "effluvia" original: "effluviis"; these were thought to be tiny particles or flows emitted by objects sent out from the object—nevertheless, it is demonstrated by means of the air pump original: "antliae pneumaticae"; a device used in 18th-century physics to create a vacuum that if a sound-producing instrument is placed in a space void of air, so that it has absolutely no communication with the air, no sound at all can be perceived, no matter how close you approach. However, as soon as air is allowed to enter, the sound is heard again. From this it follows that the air and the change produced in it by the sound-emitting instrument are the true and immediate cause of sound.

§. 3. To make it clear what this change and modification of the air is that excites the sensation of sound, it is useful to consider a specific case in which sound is produced and to investigate the resulting effect in the air. For this reason, let us look at a stretched string original: "chordam tensam" which, when plucked, emits a sound. By plucking the string, nothing else is produced except a trembling motion original: "motus tremulus"; what we would now call vibration, by which the string wanders very rapidly back and forth beyond its position of rest within its own boundaries. In thicker strings, this motion is easily perceived even by the eyes; in thinner ones, even if it cannot be seen, there is no doubt that it is present. Furthermore, anyone who touches a ringing bell with their hand will feel it trembling all over.