It may be well to point out that from this ultimate datum of science--or rather, let us say, of experience--there follows a deductive explanation of the law of causation. For this law, when stripped of all the metaphysical corruptions with which it has been so cumbersomely clothed, simply means that a given collocation of antecedents unconditionally produces a certain consequent. But this fact, otherwise stated, amounts to nothing more than a re-statement of the ultimate datum of experience--the fact that energy is indestructible. For if this latter fact be granted, it is obvious that the so-called law of causation follows as a deductive necessity--or rather, as I have said, that this law becomes but another way of expressing the same fact. This is obvious if we reflect that the only means we have of ascertaining that energy is _not_ destructible, is by observing that similar antecedents _do_ invariably determine similar consequents. It is as a vast induction from all those particular cases of sequence-changes which collectively we call causation that we conclude energy to be indestructible. And, obversely, having concluded energy to be indestructible, we can plainly see that in any particular cases of its manifestation in sequence-phenomena, the unconditional resemblance between effects due to similar causes which is formulated by the law of causation is merely the direct expression of the fact which we had previously concluded. It seems to me, therefore, that the old-standing question concerning the nature of causation ought now properly to be considered as obsolete. Doubtless there will long remain a sort of hereditary tendency in metaphysical minds to look upon cause-connection as "a mysterious tie" between antecedent and consequent; but henceforth there is no need for scientific minds to regard this "tie" as "mysterious" in any other sense than the existence of energy is "mysterious." To state the law of causation is merely to state the fact that energy is indestructible. And from this there also arises at once the explanation and the justification of our belief in the uniformity of nature. If energy is, in its relation to us, ubiquitous and persistent, it clearly follows that in all its manifestations which collectively we call nature, similar preceding manifestations must always determine similar succeeding manifestations; for otherwise the energy concerned would require on one or on both of the occasions, either to have become augmented by creation, or dissipated by annihilation. Thus our belief in the uniformity of nature, as in the validity of the law of causation, is merely an expression of our belief in the ubiquitous and indestructible character of energy.