reference to the earth's radius; also, whether the temperature of bodies has any influence on their weight; but on these points it may be truly said that if any difference were discovered it would not be expressed by saying that the amount of matter was different, but simply that "weight" was not so fundamental and inalienable a property of matter as has been sometimes assumed; in which case it is clear that there must be a more fundamental property to which appeal can be made in favour of constancy or persistency or conservation. Now the most fundamental property of matter known is undoubtedly 'inertia'; and the law of conservation would therefore come to mean that the inertia of matter was constant, no matter what changes it underwent. But, then, inertia is not an easy property to measure,—very difficult to measure with great accuracy: it is in practice nearly always inferred from weight; and in terms of inertia the law of conservation of matter cannot be considered really an experimental fact; it is, strictly speaking, a reasonable hypothesis, an empirical law, which we have never seen any reason to doubt, and in support of which all scientific experience may be adduced in favour.

It is possible, however, to grant to Professor Haeckel—not positively, but for the sake of argument, and giving him the benefit of our present ignorance—that it is unlikely that matter in its lowest denomination can by us be created or destroyed. For, although it is now pretty well known that atoms of matter are not the indestructible and immutable things they were once thought (seeing that, although we do not know how to break them up, they are liable every now and then themselves to break up or explode, and so resolve themselves into simpler forms), yet it can be granted that these simpler forms are likewise themselves atoms, in the same sense, and that if they break up they will break up likewise into atoms: or ultimately, it may be, into those corpuscles or electrons or electric charges, of which one plausible theory conjectures that the atoms of matter are really composed.

Supposing an atom thus broken up into electrons, its weight may possibly have disappeared. We simply do not know whether weight is a property of the grouping called an atom, or whether it belongs also to the individual ingredients or corpuscles of that atom. There is at present no evidence. But whether weight has disappeared or not, it is quite certain, for definite though rather recondite theoretical reasons, that the inertia would not have disappeared; and accordingly it may be held, and must be held in our present state of knowledge, that the constancy of fundamental material still holds good, even though the atoms are resolved into electric charges—an amount of destruction never contemplated by those chemists and physicists who promulgated the doctrine of the conservation of matter.

Electrical Theory of Matter.

But then, on the electrical theory of matter, even inertia is not the thoroughly constant property we once thought it. It is a function of velocity for one thing, and when speeds become excessive the inertia of matter rises perceptibly in value. The fact that it would rise in value by a calculable amount, and that the rise would be perceptible when the speed of motion approached in value to within, say, a tenth of the velocity of light, was predicted mathematically;¹ and now, strange to say, it has recently become possible to observe and actually measure the increase of inertia experimentally, and thus to confirm the electrical theory not only as qualitatively or approximately true, but as completely and quantitatively accurate. A remarkable achievement all this! of quite modern times, which has not excited the attention it deserves—save among physicists.

But even this is not all that can be said as to the fluctuating character of that fundamental material quality "inertia." It appears possible, if electrons approach too near each other, so as to encroach on each other's magnetic field as they move, that then their inertia may fall in value during the time they are contiguous. No experimental fact has yet suggested this at present: it is improbable that even in the tightest combinations they ever really approach close enough to each other to make the effect appreciable in the slightest degree; still, strictly speaking, the inertia of matter is a known mathematical function of the distance of electrons apart, compared with their size, as well as of their absolute speed through the ether; and hence it may be found to vary from either of two distinct reasons. Nevertheless, even this variation would not be expressed as a failure in the conservation of matter, though there is now no single material property that can be specified as really and genuinely constant. So long as the electric centres of strain, or whatever they are—so long as the electric charges themselves—continue unaltered, we should prefer to say that at least the basis of matter was fundamentally conserved.

Further than this, however, we cannot go; and to say, as Professor Haeckel says, that the modern physicist has grown so accustomed to the conservation of matter that he is unable to conceive the contrary, is simply untrue. Whatever may be the case in real fact, there is no question with respect to the possibility of conception. The electrons themselves must be explained somehow; and the only surmise which at present holds the field is that they are knots or twists or vortices, or some sort of either static or kinetic modification, of the ether of space—a small bit partitioned off from the rest and individualised by reason of this identifying peculiarity. It may be that these knots cannot be untied, these twists undone, these vortices broken up; it may be that neither artificially nor spontaneously are they ever in the slightest degree changed. It may be so, but we do not know; and it is quite easy to conceive them broken up, the identity of the electron lost, its substance resolved into the original ether, without parts or individual properties. If this happened, within our ken, we should have to confess that the properties of matter were gone, and that hence everything that could by any stretch of language be called "matter" was destroyed, since no identifying property remained. The discovery of such an event may lie in the science of the future; it would be an epoch-making event in the history of science, but no physicist would be upset by it—perhaps not even surprised; nor would any one have good reason to be astonished if the correlative phenomenon occurred, and under certain conditions some knots or strains were some day caused in the ether, which had not been previously there; and so "matter," or the foundation of matter, artificially produced. In other words, the destruction and the creation of matter are well within the range of scientific conception, and may be within the realm of experimental possibility.

Persistence of the Existent.

Is there, then, no meaning in the conception which Professor Haeckel and others have so enthusiastically formulated, and which certainly commends itself to every one as representing in some sense a genuine truth, whether it be called a "law of substance" or whatever it be called? There does seem a certain plausibility in the idea, pure guess or assumption though it be, that anything which really and fundamentally exists, in a serious and untrivial and non-accidental sense, can be trusted not suddenly to go out of existence and leave no trace behind. In other words, there seems some reason to suppose that anything which actually exists must be in some way or other perpetual; that real existence is not a capricious and changing attribute: arbitrary collocations and accidental relations may and must be temporary, but there may be in each a