ON MATTER AND ETHER,

OR THE

SECRET LAWS OF PHYSICAL CHANGE.

INTRODUCTION.

SINCE the discovery of the Law of Gravitation, by Sir Isaac Newton, an immense progress has been made in every branch of physical science. Chemistry and electricity were then in their infancy, and galvanism quite unknown. But the advance, of late years, has been rapid and continual. Secondary laws of high importance have been discovered, as in the Undulatory Theory of Light, researches on specific and radiant heat, electrical attraction and induction, atomic proportions, and the laws of crystallization. All the subtler influences of nature, light, heat, electricity, magnetism, chemical affinity, crystalline polarity, are found, more and more, to be intimately related to each other. Men of science feel themselves to be on the verge of some great discovery, but the key which can unlock these various secrets of nature has not yet been attained.

The theories which have been proposed, to explain separately some one class of these phenomena, are plainly insufficient. Thus electricity has been referred, sometimes to one, and sometimes to two electric fluids. The second hypothesis has been developed by Coulomb, Poisson, Whewell, Murphy, and other analysts. But the reasons why these two fluids should combine with matter, and nearly all their laws of combination, remain wholly unexplained; while the supposition itself, of two such fluids differing only by a positive and negative sign, is very remote from natural probability. Again, magnetism has been referred, by Ampère, to spiral systems of electric currents. But the needful postulates, that two elements of electricity attract each other, when they move in the same direction at right angles to the line of junction; that they repel with the same force, when they move opposite ways, and with half the force, when the motion is in the direction of their distance, have none of the simplicity of ultimate laws. No explanation at all is given, why electricity in motion should attract differently from its state of rest, or why currents in constant revolution should exist around the particles of a magnet. The theory may have its use as a landing-place in the ascent of science, but the true nature both of electricity and magnetism clearly remains still to be discovered.

Again, theories of heat have been constructed, by Fourier and others, with great analytical ability, on the hypothesis that caloric is a fluid, condensed around the molecules of matter, and radiating constantly from one part of it to another. But the later discoveries of the Polarization of Heat, and of its equivalence with mechanical force, have almost entirely overthrown the idea that it is a

distinct and separate fluid. All these theories, of two electric fluids, a magnetic fluid, and a fluid of heat, are not only fragmentary, but divergent, and in their results contradictory to each other.

Several attempts have been made to propound some view of the constitution of matter, which may account for the various forms of molecular action. The theory of Boscovich was one of the earliest. Each particle was supposed to be a point, endued with attractive and repulsive force; the curve of force being such as to cross the axis several times, or to have several neutral distances, where the force changes from attraction to repulsion, the repulsion tending to infinity at one limit, and the attraction varying as the inverse square at the other. But a law of force with these conditions is so complex, and admits of so many arbitrary varieties, as to make the hypothesis highly improbable, and practically useless. The modern discoveries in optics, also, seem to exclude the notion that one kind of matter alone will account for all the varied phenomena of the universe.

The first rule of philosophical reasoning, laid down by Sir Isaac Newton, is to this effect: "No more causes of natural things are to be admitted, than such as are both true, and sufficient to explain their appearance." He says further, at the close of the work: "Whatever is not deduced from the phenomena is to be called an hypothesis; and hypotheses, whether metaphysical or physical, whether of occult qualities or mechanical, have no place in experimental philosophy."

The rule, thus stated, is clearly open to a very weighty objection. If the true cause is already known, all inquiry is superfluous. But if not known, how can it be the test

of a sound induction? Dr Whewell has observed, more accurately, that hypothesis is essential to the progress of science; that few discoveries have been made, till several hypotheses have been tried; and that the test of a sound induction is not the rejection of all hypothesis, but a readiness to invent those which shall be most promising, and to abandon those which have been proved insufficient. It is like the use of a bunch of keys in unlocking a door. He succeeds best who only tries the keys which have some apparent resemblance of size to the lock itself, and who, instead of trying to force the lock with a wrong key, lays it aside quickly, and tries another. There can be no more complete test of an hypothesis than its power to explain all the phenomena; and the word "true" in Newton's rule, may thus appear not only superfluous, but to involve a logical contradiction. The real meaning, however, of Newton, was probably this; that a cause already accepted for one class of phenomena, if it will also explain another class, is preferable to one which explains the latter alone. Thus gravity was a known fact with regard to bodies on the earth's surface; and since it would account also for the moon's revolution, and the orbits of the planets, it was to be preferred to any explanation which would apply to the latter only. The principle, thus understood, is the same which has been well called "the consilience of inductions," and seems to lead to the following principles or rules of inductive inquiry.

AXIOM I. There are only two tests of the truth of any physical hypothesis; its fitness to account for all the phenomena, and its simplicity.

AXIOM II. The simplest hypothesis, which offers any hope of explaining the facts, ought first to be tried; and

more complex ones, only when the simpler has been tried, and proved to be insufficient by careful examination.

AXIOM III. The first step in the required proof of any hypothesis, is when it can be shewn to produce, by natural consequence, all, or nearly all, the same classes of phenomena, which a true theory is wanted to explain. Such an hypothesis may be called probable, and has a claim to fuller development.

AXIOM IV. An hypothesis is not only probable, but almost certainly true, when, on being developed, it yields a large variety of measurable results, which agree in quantity with the results of direct experiment.

AXIOM V. The simplest hypothesis is that which includes the smallest number of arbitrary postulates, such as distinct laws of force, constants of force, and constants of distance.

The first result of these simple axioms, when applied to the great problem of physical science, still unsolved, is to sweep away all the specific fluids, which have been conjecturally proposed, each for one limited class of phenomena; the two electricities, the fluid of heat, or caloric, and the magnetic fluid. The phenomena of optics seem to compel the admission of a luminous ether, besides matter, of immense elastic force. Until it has been shewn that this double admission, of ponderable matter, and of luminiferous ether, is insufficient to explain the phenomena, the recognition of any further varieties, or of fundamental diversities in matter itself, or of many distinct and unchangeable material substances, is opposed to the true laws of a sound