is a legitimate enough generalisation: we do not really doubt its conservation and constancy when we admit that we are not yet sure of having fully and finally exhausted the whole category of energy. What we do grant is, that it may hereafter be possible to discover new forms; and when new forms are discovered, then either the definition may have to be modified, or else the detailed statement at present found sufficient will have to be overhauled. But after all, this is not specially important: the serious mistake which people are apt to make concerning this law of energy is to imagine that it denies the possibility of guidance, control, or directing agency, whereas really it has nothing to say on these topics; it relates to amount alone. Philosophers have been far too apt to jump to the conclusion that because energy is constant, therefore no guidance is possible, so that all psychological or other interference is precluded. Physicists, however, know better; though unfortunately Tyndall, in some papers on Miracles and Prayer, thoughtlessly adduced the conservation of energy as decisive. This question of "guidance" is one of great interest, and I emphasise the subject further on, especially in Chapter IX.
Conservation of Matter.
Take next the "conservation of matter"—which means that in any operation, mechanical, physical, or chemical, to which matter can be subjected, its amount, as measured by weight, remains unchanged; so that the only way to increase or diminish the weight of substance inside a given enclosure, or geometrically closed boundary, is to pass matter in or out through the walls.
This law has been called the sheet-anchor of chemistry, but it is very far from being self-evident; and its statement involves the finding of a property of matter which experimentally shall remain unchanged, although nearly every other property is modified. To superficial observation nothing is easier than to destroy matter. When liquid—when dew, for instance—evaporates, it seems to disappear, and when a manuscript is burnt it is certainly destroyed: but it turns out that there is something which may be called the vapour of water, or the "matter" of the letter, which still persists, though it has taken rarer form and become unrecognisable. Ultimately, in order to express the persistence of the permanent abstraction called "matter" clearly, it is necessary to speak of the "ultimate atoms" of which it is composed, and to say that though these may enter into various combinations, and thereby display many outward forms, yet that they themselves are immutable and indestructible, constant in number and quality and form, not subject to any law of evolution; in other words, totally unaffected by time.
If we ask for the evidence on which this generalisation is founded, we have to appeal to various delicate weighings, conducted chiefly by chemists for practical purposes, and very few of them really directed to ascertain whether the law is true or not. A few such direct experiments are now, indeed, being conducted with the hope of finding that the law is not completely true; in other words, with the hope of finding that the weight of a body does depend slightly on its state of aggregation or on some other physical property. The question has even been raised whether the weight of a crystal is altogether independent of its aspect: the direction of its plane of cleavage with 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