physical speculations upon the nature of Form and Matter, Bound and the Boundless; and shall merely observe that the system would naturally tend to resolve all the qualities of Matter into the primary ones of its extension or Form, and the absolute hardness or Impenetrability of its component parts.

Besides the obvious formal qualities of matter, there are certain other secondary qualities, which may be termed supposititious, conventional, or occult,* inasmuch as the words Elasticity Colour, Inertia, Gravity, and many others,

* I use the word supposititious, which implies spurious, as well as hypothetical, in preference to occult, not only to avoid offence, but in better keeping with what I have written upon theory and hypothesis. The word secondary, has been used: but it neither expresses the meaning intended to be conveyed, nor includes under it all the qualities which it ought. The word occult, as well known, would perhaps be better, but it has been sadly abused. The occult qualities, however, of Aris totle are not the nonsense usually fathered upon him. He uses the words Gravity, for instance,

are words conventionally assumed to express certain phenomena themselves, or the unknown causes of such phenomena, which have been traced no higher, but which still remain desiderata, to which the attention of science should be directed. They may perhaps be resolved into some immediate formal cause, or into several intermediate links in the chain of efficient causes, or latent processes. But it should never be forgotten, for a moment, that these words, expressive of what are called the qua

and Levity, precisely as we do ourselves in reference to heavy and what we call imponderable bodies, expressly however denying them to be occult qualities or virtues; and endeavours to seek the causes not only of these, but of the properties of the Loadstone, and of the Inertia of Projectiles: and, however nugatory his attempt, it is evident from the attempt itself, that he never dreamt of advocating such doctrines as have been imputed to him. Again, with respect to the abhorrence of a Vacuum, I verily believe there is not one syllable upon the subject throughout his works. See VIII. Phys. 4. 10-III. De Cœlo 2-IV. Met. 14.

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lities and properties of matter, in themselves, convey no explanations, but are merely assumed, conventionally, from the necessity, which our ignorance imposes upon us, to use some stated general terms as names for the unknown causes of certain classes of phenomena, the individual phenomena of which classes, however they may differ among themselves in some respects, have nevertheless certain similarities, which obviously point them out as the effects of one and the same kind of cause. If we mean any thing further by the words, we wilfully deceive ourselves. If we really imagine that bodies are attracted by Attraction, we should be equally justified in accounting for their lightness by Levity, for their cohering by Cohesion or Suction, for their parting from one another by Partition, or by any barbarous term it might be our good pleasure to coin: for nothing is easier than to convert the verb, expressive of the effect, into a corresponding

substantive. The words are nevertheless extremely convenient, and are not lightly to be rejected, but must be gradually laid aside as the real causes are ascertained: thus we have laid aside the term Levity as a supposititious Cause, having at length revolved the phenomena of lightness into those of Gravity, confirming the hypothesis of Timæus. In like manner, the word Suction has almost been forgotten, by the resolution of the phenomena of the pump into the weight of the incumbent air. Sir Isaac Newton attempted to resolve the Elasticity of light, as far as it concerned reflection, into a latent process, the attractions of a fluid upon the surfaces of bodies and if he had succeeded, the word Elasticity would, long ere this, have been lost to us as a supposititious cause.

With respect to the Qualities of matter, we are led, by all the Analogies of nature, to suppose that they may be resolved either into formal causes, or into

phenomena depending upon motion: and it must be our grand object to ascertain the real causes corresponding to the words we use to express them; and gradually to expel those phrases, with which philosophy is overrun. I must, however, defer the further examination of them till I speak of the Efficient causes, to which they more properly belong.

In the phenomenon of COLOUR, which comes more properly under this division, the Metaphysical distinction drawn between the Sensation and Perception by the Mind and the Quality of the body, which was the cause of that perception, -between the redness, with which the senses are affected, and the supposititious quality of the body, which so operates upon light as to produce that sensation and perception, cleared away several strange incumbrances. But the grand discovery that redness or any other colour may communicated to bodies by the mere

be