Returning to the general question, we find the results to be:—that we have positive experience of the continued existence of Matter; that the form of our thought renders it impossible for us to have experience of Matter passing into non-existence, since such experience would involve cognition of a relation having one of its terms not representable in consciousness; that hence the indestructibility of Matter is in strictness an _à priori_ truth; that nevertheless, certain illusive experiences, suggesting the notion of its annihilation, have produced in undisciplined minds not only the supposition that Matter could be conceived to become non-existent, but the notion that it did so; but that careful observation, showing the supposed annihilations to have never taken place, has confirmed, _à posteriori_, the _à priori_ cognition which Psychology shows to result from a uniformity of experience that can never be met by counter-experience. * * * * * § 68. The fact, however, which it most concerns us here to observe, is, the nature of the perceptions by which the permanence of Matter is perpetually illustrated to us, and from which Science draws the inference that Matter is indestructible. These perceptions, under all their forms, amount simply to this—that the _force_ which a given quantity of matter exercises, remains always the same. This is the proof on which common sense and exact science alike rely. When, for example, somebody known to have existed a few years since is said to exist still, by one who yesterday saw him, his assertion amounts to this—that an object which in past time wrought on his consciousness a certain group of changes, still exists because a like group of changes has been again wrought on his consciousness: the continuance of the power thus to impress him, he holds to prove the continuance of the object. Should some auditor allege a mistake in identity, the witness is admitted to give conclusive proof when he says that he not only saw, but shook hands with this person, and remarked while grasping his hand, that absence of the index finger which was his known peculiarity: the implication being, that an object which through a special combination of forces, produces special tactual impressions, is concluded still to exist while it continues still to do this. Even more clearly do we see that force is our ultimate measure of Matter, in those cases where the shape of the matter has been changed. A piece of gold given to an artizan to be worked into an ornament, and which when brought back appears to be less, is placed in the scales; and if it balances a much smaller weight than it did in its rough state, we infer that much has been lost either in manipulation or by direct abstraction. Here the obvious postulate is, that the quantity of Matter is finally determinable by the quantity of gravitative force it manifests. And this is the kind of evidence on which Science bases its