proper nature. A child would never dream that one identical force lies behind the energies which work such various wonders. Can it be the same force which is flashing out vividly in the lightning; which is bubbling, singing, burning him, pushing up the lid, shaking the whole stove, and sending out torrents of steam from the spout of the furiously boiling tea-kettle; which is whirling and humming in his spinning top, which gives his top its color and its form and holds its minutest parts together as a firm and compact wood that stoutly resists both his small fingers and his jack-knife; and is it the same force which is streaming down to him in sunbeams that warm, light, beautify, and give vital energy to every living thing? Yes, it must be.

All force is force; it is power to act, to produce changes; there is no term in any language that is more simple or more forcible in which to express it. It is a term so generic that it must embrace not only all physical but all mental energies as well; so that we obtain a realizing sense of what it is in kind, more from personal experience and from our own ability to will and to do, than from any other mani

festation of it. Yes; force is force pure and simple; one, but not indivisible.

All water is water, and possesses the whole nature of water in all respects, down not only to the smallest drop, but down even to the smallest division which can possibly be made and yet leave the structure of the substance unchanged. But vapor and ice are both equally water; yet the energies which manifest themselves in the fluid, the solid, and the vapor respectively, are curiously unlike, working all of them by different processes. It is the same force remaining, each portion of it, with its own least particle of the substance; but the mode in which the force acts varies greatly in each of the three forms of water. As all the conditions vary, so the mode of the force varies; and the force modifies the form of the substance in which it inheres as it is itself modified in its action. The least division of body and the least division of force can never part company.

The total sum of variable conditions determines both the mode and the amount of energy which shall be called into present manifestation; but these con

ditions themselves depend upon prior energies. All action arises out of some former activity, and the series of changes thus remains everywhere unbroken.

All force must be regarded as always in action. We may run backward indefinitely to the beginning of the present constitution of the universe (supposing the present order of Nature to have had a beginning, as I reason that it must have had) and we shall find that the same force has been forever changing its modes or forms of energy, and that these modes arise one out of another in an unbroken series of changes.

It must follow not only that the total of force has produced a total series of continuous changes; but it follows also that each least division of force must have been producing a small continuous series of its own. It must itself have taken part in one unbroken process of changes. No smallest division of force could be exempt from this necessity. the smallest possible division of force must be regarded as the true centre of force which is not susceptible of division without utter annihilation.

But

MODES OR ENERGIES OF FORCE.

Energies as related to work.-Different types of energies; as heat, electricity, etc.-All energies have a twofold action.—Transformation of energy.-Equal exchange of energies.-Energies are of two classes.-Coöperative action of several forces.-Action of resistance to motion.-Pendulum-like vibrations of the ether in transmission of light.-Electricity.-Conditions influence the action and exchange of energies.-Forces are never exchanged.

A

CTIVE or working force has been called energy

"to distinguish it from non-working force;" but if all force is active or working force in reality, then the distinction lies only in the fact that the one class can be made available by mankind in the furtherance of desirable ends, while the other cannot. Thus the carbon which is stored away in coal possesses itself a store of inherent force, which, when once ignited, can go on uniting with the oxygen of the air to produce heat. This joint action of the forces in coal and oxygen is called energy because it is said to do work, that is, to produce the desired heat. The action and reaction between a definite mode of force in coal and another mode of force in

the oxygen of the air, by thus coöperating, produce a new mode of force called heat.

It is obvious that whenever two opposed modes. of force can together produce a third mode, by the transmutation of their joint process into a new form of process, this change is called work. Thus any transformation in kind of action, is work; and the forces which produce the change are energies. But if force is active from the necessity of its own nature as force, and if a given amount of all force is in continual coöperation with an equal amount of opposed force, then whether they produce a change in the form of the activity or not, still they are both energies in the proper sense of that term. Their joint action becomes a mode of force.

Hence I propose to define an energy to be a mode, any one of the modes, in which force coöperates. By this definition energies are not distinctively "force in action;" but they comprise all the various modes in which force can act. They are the actions or processes of force. The reason for giving a somewhat new meaning to the word energy is that change or transmutation cannot take place between