colour or the tone of one musical instrument is judged preferable to that of another in the same way by everyone.

If we assume with Euler that colours are isochronous vibrations (pulsus) of the aether, as sounds are of the air in a state of disturbance, and, — what is most important, — that the mind not only perceives by sense the effect of these in exciting the organ, but also perceives by reflection the regular play of impressions (and thus the form of the combination of different representations) which I still do not doubt — then colours and tone cannot be reckoned as mere sensations, but as the formal determination of the unity of a manifold of sensations, and thus as beauties in themselves.

But “pure” in a simple mode of