PHYSICS. The old term "natural philosophy" signified an attempt to frame a theory of that part of the material universe which could be explored by observation and experiment, and of which the underlying laws were sufficiently understood to be amenable to mathematical calculation. The science of biology was excluded from its purview, for life was not sufficiently understood to be amenable to treatment of that thorough kind, and similarly the mental sciences were excluded, although an observable mate rial organism was a sensible instrument and mode of manifesta tion; but even so the subject was a huge one and had to be sub divided. The branch of biological science nearest to inclusion was physiology, being a study of the mechanism involved in the func tions of living organisms.
The branch of natural philosophy that advanced most rapidly towards perfection was the mechanics of the heavenly bodies, where the things treated of were comparatively few and far apart, and could readily be dealt with as individuals, so that the laws governing their movements could be formulated with some satis faction. This branch, under Sir Isaac Newton, became so highly elaborated as to dominate and set an example to the rest ; but, after all, astronomy was only a special case of the motion of ma terial bodies, and Galileo had begun the study of ordinary motions on the earth's surface, developing into a complete treatment of their velocities, accelerations and distortions, and partly account ing for them by the fundamental inertia of matter influenced by forces of different kinds, and by the subsidiary properties of elas ticity, friction, cohesion and the like.
Matter was always known to exist in three states, solid, liquid and gaseous, each having peculiar properties of its own; and the fluids formed resisting media through which the solids could move. Moreover all these bodies were subject, not only to locomotion in bulk, but to internal vibrations, and for the apprehension of these vibrations we had special sense organs, which enabled them to be examined with special facility, and thereby taught us much con cerning the things themselves. Some of these vibrations are known as sound, others as heat, and there was yet a third kind of vibra tion, appealing to the eye, the effect of which could travel across space empty of matter, which therefore had to be filled with a hypothetical substance called "the ether" (or aether), whose prop erties are still in doubt.
Apart from these vibrations, which could be originated and ab sorbed by matter, it was found that matter consisted of particles called atoms, of a definite size and weight, which could enter into combination with each other, and so form the various compounds with which humanity had always been acquainted. A study of this branch of natural philosophy blossomed into the great science of chemistry, while geology took over a study of the history and con ditions of the earth's crust. The remaining portions of natural philosophy were grouped in comparatively modern times under the head physics, which, by derivation from signifies a study of nature so far as it can be reduced by calculation and ex periment to a few simple or at least fundamental laws. Those laws, first studied by Galileo, were formulated with masterly pre cision by Isaac Newton, and throughout the 19th century domi nated the field. It was hoped at one time that they would be all inclusive ; the expressed ambition of Newton was that ultimately all observable phenomena might be brought under their sway. A long continued effort was made throughout the 19th century to apply them, not only to matter, but to the ether also—an attempt which failed, and has now, for a time at any rate, been abandoned. Hypothetical attempts were also made to include the phenomena of life and mind under the same fundamental laws of mechanism, without necessarily postulating anything outside and beyond such treatment ; these efforts, the basis of a materialistic philosophy, were perfectly legitimate, though they have proved unsuccessful. No one claims that the ordinary laws of physics and chemistry are disobeyed by live things, but it is now fairly admitted that they have to be supplemented, while, with regard to the ether, it is still a question as to how far the simple laws are applicable at all. The very terms inertia, velocity, acceleration, force, are of only doubtful validity except when applied to definite material par ticles, and even then these properties themselves require elucida tion. It may be that no fundamental explanation of even the sim plest phenomenon can be satisfactorily and safely given until the laws of the fundamental substance, of which probably matter it self is composed, are better understood and formulated.