Force, energy, or power, whatever it may be, yields the central conception out of which the questions referred to spring. It supplies a ground, and is a datum, required and used alike by the most materialistic among scientific workers and the most speculative. It is destined, as regards matters lying between physical and mental science, to be the ground of conciliation, perhaps of reconciliation. No reality occupies a more undisputed position than force. But few, if any, truths of its class are better established by all the might and main of science than its immateriality. It is not matter, and yet it has a real existence. It is no figment of the imagination. Besides this, in the principle of the persistence or conservation of force, is laid, so far as science can do it, the proof of its indestructibility.

In the discussion which follows we may safely assume the substantial, independent reality of matter as against the Idealist. On the other hand, once grant the indestructible, immaterial something called force, and spirit can take care of itself. Immaterial" entities" need be insisted on no longer. One is conceded, and, so far as it seems susceptible of proof by the methods of physical science, it is proved.

While the question more immediately before us is not the correlation and conservation of what are called physical and chemical forces, yet a brief historical résumé of the progress of research and opinion in this relation may prove useful. Whether to M. Seguin, or Count Rumford, or Dr. J. P. Joule, or Mayer of Heilbronn, or to others, science is most indebted, or who should have the credit of priority in the discovery of the nature and relations of the physical forces, are questions upon which it is not necessary for us to enter.

The discovery that may be fairly looked upon as introductory to the doctrine we are soon to state, was that announced by Count Rumford (Professor Thomson) in a paper to the Royal Society of Great Britain in 1798. Up to that time heat had been regarded as a subtle or fluid form of matter; but, as the result of rigorous experiments, he concluded it could not "possibly be a material substance." He says, "It appears to me to be difficult, if not impossible, to form any distinct idea of any thing capable of being excited or communicated in these experiments unless it be MOTION."-Introduction to Youmans's Correlation and Conservation of Forces, p. 33. Fifty years later Dr. J. P.

Joule, of Manchester, England, proceeding on much the same line, established by a long series of delicate and elaborate experiments what is called the "heat unit," or "mechanical equivalent" of heat. By these latter experiments it was clearly determined that the force or energy represented by a weight of 772 pounds falling through a distance of one foot would produce, and could be made to produce, an amount of heat sufficient to raise the temperature of a pound of water one degree Fahrenheit. In this way it was shown that mechanical energy could be converted into heat, while the converse of this was established on a large scale in the discovery of the steam-engine.

The discovery by Oersted, that electrical can be converted into magnetic force, and the converse at a later day by Faraday, led the way to others, until in process of time the whole list of "imponderables" was drawn into the seemingly closed circle of correlation, as mutually convertible inter se. The history of the successive discoveries on which this brilliant generalization depended would be interesting, but it is aside from our present purpose to recite it. The results may be formulated as follows:

1. It is alike impossible to create or destroy physical force or energy.

2. Where force disappears in one form, it is only to reappear without increase or diminution in some other.

The first is called the law of conservation, the second, the law of correlation, of forces.

Examples might be easily given under both these laws, especially the latter, which would be full of interest; but they have been given already in so many ways to the public it is deemed unnecessary. But we may say with confidence, no facts in science so general in their nature seem to be better established than the conservation and correlation of forces.

But it could not be expected investigation would rest here. Questions similar to the following would inevitably arise: Since the various forms of physical and chemical force are mutually convertible, which form shall be selected as the representative or parent of the rest? Which shall be set down as primary, and which as derivative? In point of fact, as Mr. Grove says, (Youmans's "Conservation and Correlation of Forces," p. 185,) "The evolution of one force or mode

of force into another has induced many to regard all the different natural agencies as reducible to unity, and as resulting from one force, which is the efficient cause of all the others. Thus one author writes to prove that electricity is the cause of every change in matter; another, that chemical action is the cause of every thing; another, that heat is the universal cause, and so on.'

Again, What is the source of these forces? From what fountain do they spring? What relation have they to matter? What are their relations to "life" and "mind?" Are the forces called "life force" and "mental force" independent of, and distinct from, the physical and chemical forces? or are they at root the same, differing only in modes or "conditions" of manifestation? If they acknowledge a common fountain head, where is it? Is it at this end of the series or that physical, or mental, or intermediate? Are these forces simple or complex? As regards vital and mental forces, are they not dynamic compounds, similar to the living material compounds that compose the organisms of plants and animals?

In the case of plants and animals we often see elementary substances appropriated, ending with highly complex associations among them in the compounds of the living organisms. In process of time these, by natural analytic processes, are resolved back again into the primitive elements started with. Is not this true for forces as well? As material physical elements combine to form living compounds, may not dynamical physical elements also? Do not the former prefigure the latter? Materially speaking, "nothing passes into us but matter, and nothing passes out of us but matter, and nothing can be got from us after we are dead but matter, and this matter does not come down to us, but up from simpler, more elemental states below."

These elements and compounds enter our organisms freighted with energy or force. Does not all the energy of our bodies, even "vital" and "mental," slip in, and steal back this way? Are the differences between the physical and chemical forces, and the so-called "vital" and "mental" forces, any more marked than those which separate oxygen, carbon, hydrogen, and nitrogen from the protoplasm or muscle which they compose? Questions like these, many of them only deliberate con

clusions in the interrogative form, have come up, and have been variously answered. Some have affirmed that the physical, vital, and mental forces belong to distinct categories. Others have affirmed with various degrees of positiveness that they have a common origin, the special differences being but the masks that hide their oneness. Strip these away and they are seen, however widely they may differ phenomenally, to be but the varied play of the same primal energy. As matter in its elemental states, or simplest combinations in the physical world, is the great storehouse from which living beings draw the materials for the growth and development of their organisms, so in regard to the development and growth of their forces, whether "vital" or "mental." As the simple dead matter is elevated into complex living matter, so with the forces. This material development, or "evolution," which is always upward, never downward-from the simple to the complex-from the "homogeneous" to the "heterogeneous"-it is said aptly figures, is indeed a registry in material terms of what takes place among forces. The source, then, of all the forces, as of the matter, of living beings, is the physical world-is physical force. This is the common and exhaustless treasury from which all forms of force, whether "vital" or "mental," are either directly or indirectly drawn. The particular form it exhibits depends wholly on the "conditions" under which it "works."

Here it is manifested in the microscopic fungus, there in the gigantic growths of our forests; here in the animalcule, there in the elephant or whale. Here it binds together by chemical attraction two invisible, simple atoms, to form an equally invisible compound atom of water; there it binds together the unnumbered millions of suns, planets, nebulæ, and systems throughout the fathomless profundities of space. Here it is manifested in the fall of an apple or a stone; in the ripple on a pond or a storm on the great deep; in the gentle breeze, in the hurricane, in the play of the golden willow in the wind, in the earthquake or the thunder-stroke; there in the repulsions of antipathy or hatred, or the attractions or "affinities" of friendship or of love. This latter is a favorite mode at present of answering the questions above raised. It is to this answer, in some of its phases and consequences, we desire to call attention in the following pages.

That there are forms of force or energy called "vital" and "mental," at least as different from physical and chemical forces as these are from each other, there can be no real question. Accepting fully and heartily as a fact, the correlation of the physical and chemical forces, it is our intention to inquire what the grounds are for affirming the "vital" and "mental" forces are "correlated" with the physical and chemical. Two questions present themselves. First, Who holds to the opinion just referred to, and on what evidence does it rest? and, second, What is the origin of force?

The following are only specimens of the opinions, hopes, expectations, and imaginings of various persons, eminent in the walks of science, bearing on the subject in question.

Every particle of matter within the body obeys implicitly the laws of the chemical attractions. No overpowering or supernatural agency comes in to complicate their action, which is modified only by the action of the others. Vitality, therefore, is the sum of the energies of a living body, both potential and actual.—Barker, pp. 14, 15.... The most advanced thinkers in science of to-day, therefore, look upon the life of the living form as inseparable from its substance, and believe that the former is purely phenomenal, and only a manifestation of the latter.-Barker, p. 5, et seq.

Heat, light, chemical affinity, etc., are alike transformable into each other and into those modes of the unknowable which we distinguish as sensation, emotion, thonght. These in their turn being directly or indirectly retransformable into the original shapes.Spencer, F. P., p. 280. . . . Any hesitation to admit that between the physical forces and the sensations there is a correlation like that between the physical forces themselves, must disappear on remembering how the one correlation, like the other, is not qualitative but quantitative.... Besides the correlation and equivalence between external physical forces and the mental forces generated by them in us under the form of sensations, there is a correlation and equivalence between sensations and those physical forces which, in the shape of bodily actions, result from them.-Spencer, F. P., p. 275.... That no idea arises, save as a result of some physical force expended in producing it, is fast becoming a common-place in science, and whoever will duly weigh the evidence will see that nothing but an overwhelming bias in favor of a preconceived theory can explain its non-acceptance.-Spencer, F. P., p. 280.

That these forces (mechanical, thermal, luminous, electric, chemical, nervous, sensory, emotional, and intellectual) are perfectly co-ordinated-that there is some definite relation among them which explains the marvelous dynamic unity of the living organism-does not admit of question.-Youmans, Introd., xxxii. I hold, with the materialist, that the human body, like all living