This extract is from the Introduction to “Nouvelles réflexions sur le principe sonore” in Code de musique pratique, Paris, 1760, p.189.
One principle governs everything. Any thinking person will have sensed the truth of this, though no one has yet explained it. In the conviction that there must be a universal principle, the earliest philosophers turned to music in their search for it. Pythagoras followed the Egyptians in applying the laws of harmony to the motions of the planets. Plato believed that the disposition of the soul was governed by these laws. Aristotle, his disciple, described music as a divine and heavenly thing, and added that it provided the explanation of the system on which the world was built. So impressed were these philosophers by the marvellous way in which the constituent parts of the universe harmonise, that they continued to look for the explanation in music, as the one thing in which proportion dwelt. For those objects that are perceived by the other senses are only the image of proportion, properly speaking. Movement, action, temporal relationships, and analogies, these can only be expressed in acoustic symbols. Unfortunately the system that these great men adopted – far from bringing them nearer to the desired goal – only served to distance them further from it. There can be absolutely no doubt that they were unaware of the phenomenon of the resonant body (corps sonore).
Theory of Music 