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 pation from which Pythagoras by his numeral, and Plato by his musical, symbols, and both by geometric discipline, aimed at, as the first of the mind)—under this strong sensuous influence, we are restless because invisible things are not the objects of vision; and metaphysical systems, for the most part, become popular, not for their truth, but in proportion as they attribute to causes a susceptibility of being seen, if only our visual organs were sufficiently powerful.

From a hundred possible confutations let one suffice. According to this system the idea or vibration a from the external object A becomes associable with the idea or vibration m from the external object M, because the oscillation a propagated itself so as to re-produce the oscillation m. But the original impression from M was essentially different from the impression A: unless therefore different causes may produce the same effect, the vibration a could never produce the vibration m: and this therefore could never be the means, by which a and m are associated. To understand this, the attentive reader need only be reminded, that the ideas are themselves, in Hartley's system, nothing more than their appropriate configurative vibrations. It is a mere delusion of the fancy to conceive the pre-existence of the ideas, in any chain of association, as so many