obtains currency. In the second place, the currency of this belief continues so long as there is not such power of introspection that it can be seen what happens when the attempt is made to annihilate Matter in thought. But when, during mental evolution, the vague ideas arising in a nervous structure imperfectly organized, are replaced by the clear ideas arising in a definite nervous structure; this definite structure, moulded by experience into correspondence with external phenomena, makes necessary in thought the relations answering to absolute uniformities in things. Hence, among others, the conception of the Indestructibility of Matter.

For careful self-analysis shows this to be a datum of consciousness. Conceive the space before you to be cleared of all bodies save one. Now imagine the remaining one not to be removed from its place, but to lapse into nothing while standing in that place. You fail. The space which was solid you cannot conceive becoming empty, save by transfer of that which made it solid. What is termed the ultimate incomprehensibility of Matter, is an admitted law of thought. However small the bulk to which we conceive a piece of matter reduced, it is impossible to conceive it reduced into nothing. While we can represent to ourselves the parts of the matter as approximated, we cannot represent to ourselves the quantity of matter as made less. To do this would be to imagine some of the constituent parts compressed into nothing; which is no more possible than to imagine compression of the whole into nothing. Our inability to conceive Matter becoming non-existent, is immediately consequent on the nature of thought. Thought consists in the establishment of relations. There can be no relation established, and therefore no thought framed, when one of the related terms is absent from consciousness. Hence it is impossible to think of something becoming nothing, for the same reason that it is impossible to think of nothing becoming

something the reason, namely, that nothing cannot become an object of consciousness. The annihilation of Matter is unthinkable for the same reason that the creation of Matter is unthinkable.

It must be added that no experimental verification of the truth that Matter is indestructible, is possible without a tacit assumption of it. For all such verification implies weighing, and weighing implies that the matter forming the weight remains the same. In other words, the proof that certain matter dealt with in certain ways is unchanged in quantity, depends on the assumption that other matter, otherwise dealt with, is unchanged in quantity.

54. That, 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. 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, an object known to have existed years since is said to exist still, by one who yesterday saw it, 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. 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 de

terminable by the quantity of gravitative force it manifests. And this is the kind of evidence on which Science bases its alleged induction that Matter is indestructible. Whenever a piece of substance lately visible and tangible, has been reduced to an invisible, intangible state, but is proved by the weight of the gas into which it has been transformed to be still existing; the assumption is that, though otherwise insensible to us, the amount of matter is the same if it still tends towards the Earth with the same force. Similarly, every case in which the weight of an element present in combination is inferred from the known weight of another element which it neutralizes, is a case in which the quantity of matter is expressed in terms of the quantity of chemical force it exerts; and in which this specific chemical force is assumed to be the correlative of a specific gravitative force.

Thus, then, by the Indestructibility of Matter, we really mean the indestructibility of the force with which Matter affects us. As we become conscious of Matter only through that resistance which it opposes to our muscular energy, so do we become conscious of the permanence of Matter only through the permanence of this resistance; either as immediately or as mediately proved to us. And this truth is made manifest not only by analysis of the à posteriori cognition, but equally so by analysis of the à priori one.*

* Lest he should not have observed it, the reader must be warned that the terms " 'à priori truth" and ". necessary truth," as used in this work, are to be interpreted not in the old sense, as implying cognitions wholly independent of experiences, but as implying cognitions that have been rendered organic by immense accumulations of experiences, received partly by the individual, but mainly by all ancestral individuals whose nervous systems he inherits. On referring to the Principles of Psychology (§§ 426-433), it will be seen that the warrant alleged for one of these irreversible ultimate convictions is that, on the hypothesis of Evolution, it represents an immeasurably-greater accumulation of experiences than can be acquired by any single individual.

CHAPTER V.

THE CONTINUITY OF MOTION.

855. ANOTHER general truth of the same order with the foregoing, must here be specified. Like the Indestructibility of Matter, the Continuity of Motion, or, more strictly, of that something which has Motion for one of its sensible forms, is a proposition on the truth of which depends the possibility of exact Science, and therefore of a Philosophy which unifies the results of exact Science. Motions, visible and invisible, of masses and of molecules, form the larger half of the phenomena to be interpreted; and if such motions might either proceed from nothing or lapse into nothing, there could be no scientific interpretation of them.

This second fundamental truth, like the first, is by no means self-evident to primitive men or to the uncultured among ourselves. Contrariwise, to undeveloped minds the opposite seems self-evident. The facts that a stone thrown up soon loses its ascending motion, and that after the blow its fall gives to the Earth, it remains quiescent, apparently prove that the principle of activity* which the stone manifested may disappear absolutely. Accepting, without criticism, the dicta of unaided perception, to the effect that adjacent objects put in motion soon return to rest, all men once believed, and most believe still, that motion can pass into nothing; and ordinarily does so pass. But

*Throughout this Chapter I use this phrase, not with any metaphysical meaning, but merely to avoid foregone conclusions.

the establishment of certain facts having an opposite implication, led to inquiries which have gradually proved these appearances to be illusive. The discovery that the planets revolve round the Sun with undiminishing speed, raised the suspicion that a moving body, when not interfered with, will go on for ever without change of velocity; and suggested the question whether bodies which lose their motion, do not at the same time communicate as much motion to other bodies. It was a familiar fact that a stone would glide further over a smooth surface, such as ice, presenting no small objects to which it could part with its motion by collision, than over a surface strewn with such small objects; and that a projectile would travel a far greater distance through a rare medium like air, than through a dense medium like water. Thus the primitive notion that moving bodies had an inherent tendency to lose their motion and finally stop-a notion of which the Greeks did not get rid, but which lasted till the time of Galileo-began to give way. It was further shaken by such experiments as those of Hooke, which proved that the spinning of a top continues long in proportion as it is prevented from communicating motion to surrounding matter.

To explain specifically how modern physicists interpret all disappearances and diminutions of visible motion, would require more knowledge than I possess and more space than I can spare. Here it must suffice to state, generally, that the molar motion which disappears when a bell is struck by its clapper, reappears in the bell's vibrations and in the waves of air they produce; that when a moving mass is stopped by coming against a mass that is immovable, the motion which does not appear in sound reappears as molecular motion; and that, similarly, when bodies rub against one another, the motion lost by friction is gained in the motion of molecules. But one aspect of this general truth, as it is displayed to us in the motions of masses, we must carefully contemplate; for otherwise the doc