to be approaching even that incomparable achievement. The sunshine is already held in leash; and Mr. Crookes is driving his pith balls to and fro at will, with the sunbeams for his motive power. Certainly he can learn to measure the force which he has brought so adroitly to do his bidding.

But the comparatively dull and masked reactional energies which do nothing but resist, resist, and put on the brakes remorselessly whenever there is a stir anywhere, can never be as picturesque as the others. They are not of the pictorial class, and never can be made visible to the senses. They cannot be made the subtle, strong and obedient servants of man.

Yet they are properly energies. They accomplish a work which is mathematically the equivalent of all the marvellous work done by the energies of motion. They are the true peers and equals of the motive forces, and at any turn in the tide of affairs, they become themselves motive forces as we have ⚫ already seen; exchanging, measure for measure, the energy of resistance for an equivalent amount of the energy of motion. Thus the interacting bodies, be

tween them, never lose any thing. The sum of their added energy of motion remains unchanged, and the sum of their added energy of resistance to motion remains equally unchanged. Or, if their apparent motive energy is all carried away, and appropriated by a third body, while they are both left at rest, then this third body has returned to them its equivalent in the form of energy of resistance to motion.

In any case the body and its inherent force never part company; they remain one and inseparable, and its force is always available instantaneously to meet every possible emergency of action or reaction to which it may be subjected.

We return, then, to the position that no force acts except as the correlative of some equal and opposing force. In gravitation, the attractive force lies equally in the two attracting particles; they must draw each other forward in space, probably along some coöperating line of force; and in repulsion they thrust each other mutually asunder. The inexorable law of equal exchange, of equivalent for equivalent, enacted absolutely and under all conditions, is, as we have already seen, Nature's one

4

constant, underlying her entire system of endless change. This point of rest which is as eternal as existence itself, is the fulcrum against which we may place the lever which can raise the fact of immortal life up to the great plane of accepted science.

If all action and reaction is equal and opposite necessarily between every two interacting atoms, the innate atomic force, however various and interchangeable its modes of action, must be forever unchangeable and forever untransferable. The atom, then, must be a permanent centre of individual existence, and of individual power. And if any atom be endowed with sentient force, this living or conscious force must also persist. It is immortal life. It is unchanging personal identity. It requires an unbroken continuity in the endless series of the individual sentient experience. But with all this, there must be physical action and reaction equal and opposite between this living centre of abiding force and all the other atoms with which it stands in the closest coöperative relationship.

That force proper is not only indestructible; but that it is also untransferable from its own atomic

centre, seems to me to be susceptible of the most positive proof. It will be my aim to make this clearly evident from many various points of view; for I hold it to be the most fundamental fact which has yet been made known to us concerning the vast scheme of the existing universe.

It is a simple necessary and logical consequence of the long established law of equal action and reaction. But it may also appeal to experimental tests, and it must be made clearly evident in the light of repeated illustrations.

FORCE; WHAT IT IS AND HOW IT ACTS.*

Force a practical worker.-Principles compared wfth details.— Force as easy of apprehension as body. Is more akin to consciousness. Habits of acquiring knowledge.—Indivisible centres of force the basis of science. In what sense force is a unity. In what sense force is divisible.

HE entire subject of the correlation and con

THE of the

servation of the modes of force, appears to

many minds to be exceedingly difficult of apprehension. They regard it as highly abstract and almost metaphysical in character. Nothing but actual physical demonstration would convince them that the various energies of nature can be made known to us as simply and mathematically interchangeable. These energies do, indeed, belong to the unseen universe; we can know them only in their effects; they and the ultimate particles of matter to which they pertain and which they variously modify, causing them to change in so many mysterious ways, are all of them, when regarded singly, wholly imperceptible to our grosser senses.