By RICHARD BUDD PAINTER.

I will give a short account of some forces which influence matter in a very powerful degree.

These are Heat, Light, Electricity, Magnetism, Chemical Affinity (or chemical change), and Motion.

Of these forces, as of those of attraction and repulsion, we again can only judge by their effects. God alone knows their cause and real quality.

Until a few years ago they were supposed to be quite different things essentially, but Grove, Joule, and others have now shown them to be so co-related as to be convertible the one into the other, and hence the brilliant theory of the “Correlation of the Physical Forces.”

To show this co-relation and capacity for transformation I will give a few examples. Rub a piece of iron briskly, or repeatedly strike it with a hammer, and it will become warm. We know from this, therefore, that motion will produce heat. Or strike a lucifer match against the box, and the rapid motion of the match against the hard surface will produce sufficient heat to cause the sensitive chemical substance at the end of the match to inflame, and so to give out heat and light. Or watch a horse trotting on a hard road at night, and sparks will every now and then fly from his feet.

This is because by the rapid forcible motion of his legs the iron of his shoes every now and then comes in contact with a stone, and a minute particle of steel being struck off with great force and rapidity it becomes red-hot, and thus presents another example of how motion can be converted into heat.

These are instances of heat and light being produced by the motion of friction. But now let us look at the converse case, of heat producing motion.

Light a piece of coal, and set a kettle of water on it. The flames resulting from chemical change soon leap out, and flicker, and flare, and presently the water too becomes agitated, and boils with energetic motion, and steam rushes up into the air.

Place water in a proper machine, and the force you get from the chemical change of the coal causing the water to form steam, can make a railway train weighing hundreds of tons rush along the rails at a mile a minute.

These are familiar examples of how man may set in action the correlative forces, but instances abound universally in all creation where the correlative forces are constantly producing each other by mutual conversion, and affecting thereby all sorts of natural changes.

By the stimulus of heat and light, etc., received from the sun, motion and chemical change are compelled throughout nature, both animate and inanimate. As an example of the latter take the case of water.

The water of the seas and lakes, etc., being affected by heat moves by evaporation into the air, and afterward descends as rain or dew to perform the well-known and indispensable uses pertaining thereto.

Then as to the way in which light and heat produce movement and chemical change in plants and animals, I will also cite one example, selecting plants as being the most ready of illustration.

It is under the stimulation of light and heat that the plant grows and performs its functions; and astonishing to say, the rays, both of light and heat, which fall on the plant are absorbed into it and fixed there.

That is to say, the chemical changes necessitated in the plant by the light and heat, result in these factors of change being themselves incorporated with the new wood, etc., in such a way as to be retained there in union with the atoms of carbon and other constituents of the tissue and products of the plant. Thus fixed they may remain for ages, until the wood, etc., is itself subjected to change, and then either as wood or as coal (if turned into such) it will—if burnt—again give out that light and heat which it received and appropriated during growth.

Hitherto I have spoken of chemical decomposition only as produced by motion, and heat, and light, but now I must give a familiar instance in which you can produce great chemical change and movement amongst atoms by simply mixing two chemicals together. Add tartaric acid to a solution of carbonate of soda and a great commotion ensues, owing to the superior affinity of the tartaric acid for the soda; and which acid displaces the carbonic acid in previous union with the soda, and the latter acid is turned out and escapes by violent effervescence.

This instance is but a typical example of chemical decomposition in general, and may occur in thousands of different ways in different chemicals, and producing not only chemical transformation, but the manifestation in many cases of heat, and light, and electricity, etc.

I will next speak of electricity and chemical affinity conjointly. The electrical spark will produce heat, light, chemical change, and movement.

Faraday showed also that electricity produces magnetism, and magnetism electricity—that indeed you can not produce the one without the other.

Again, electricity will set in motion chemical affinity or decomposition, and conversely chemical change will produce heat, light, electricity, motion, etc. To show this, place pieces of zinc and copper in an acid—that is, make a voltaic battery. The acid attracts the metal and sets up chemical action, and the result is that this chemical action by producing a change of state, sets free electricity, which being conducted by “the poles” or wires of the battery can there be made manifest in the following different ways:

Bring the poles together and heat, light, motion, etc., will be produced as witnessed in the dazzling electric light.

Or, to produce chemical change only, plunge the wires constituting “the poles” of the battery into water, and wonderful to say the molecules of water will have such motion imparted to them that they will be broken up into their constituent gases; and what is most marvelous, the oxygen will always be given off at one pole and the hydrogen at the other.

This is electrolysis or electro-chemical decomposition. Numbers of compounds in solution may have the molecular states of their atoms broken up thus, by the voltaic current, and curious to say of the atoms so dissevered, as above noted, those composing a given element will always be evolved by the same pole—the positive pole or the negative pole as the case may be. Some elements, that is to say, always appearing at the positive pole and others always at the negative.

Lastly I will say a few words specially as to motion.

We saw how the motion of striking the lucifer match produced chemical change, and light, and heat. We have seen also that chemical change—that is, the movement and change of place of the infinitely small atoms of matter—could be produced by heat, and light, and electricity; and that chemical change could also itself interchangeably produce all these.

We have seen, too, that motion can be produced by heat—as by the production of steam which drives the engine; also that light can cause motion, as in the growth and nutrition of plants; and it remains only in this brief summary of an immense subject, to remind the reader that electricity and magnetism can also both of them produce motion, not merely amongst atoms, but even in large masses, by means of their attractions and repulsions. Rub a piece of sealing-wax or glass with cloth or silk, and the friction will cause such a change of state in the glass or wax as to set free electricity, and this force, thus made evident by motion (rubbing), can itself produce motion by attracting pieces of paper, etc.; indeed, by using well-known methods you may lift hundreds of pounds’ weight.

So likewise as to magnetism; it can produce motion, as we see in the oscillation of the needle of the mariner’s compass—the attraction by a magnet of iron filings, etc.

From the above short survey of this marvelous subject, it can, I hope, be understood by the reader that in the co-related forces we have a most striking—nay! miraculous instance of “continuity”—that is to say, that the force, or essence, or energy, whatever it may be and whatever you may call it, that constitutes heat, light, etc., etc., is never lost, but merely changes from one form, or kind, or state, into another, in a perpetual series of everlasting transformations, each one form being capable of producing: or changing into one or more of the others—motion, for example, being readily transformed into heat, or heat into motion, etc.

My illustrations have necessarily been scanty, and my explanations brief, but I hope I have adduced sufficient to show the unscientific that in the six correlative powers we have a protean force which is able to assume the most astounding changes and varieties of form, according to some mechanical law we are totally unacquainted with.

But what is the real nature of this force or forces?

As to this I can say but little: it is one of the mysteries of creation. Experiment demonstrates that heat and light are kindred in their mechanical constitutions, and that they consist of vibrations of a “something” which is called ether, and it seems pretty certain that this “wave theory” is correct; but why they vibrate we do not know.

Then of the nature of magnetism and electricity we know even less, and can only say they are changes of the state of “something” which produces changes in the state of other things, both of matter and forces.

Some persons have thought that whereas light consists probably of the vibrations of “ether” in a particular manner, so, that electricity and magnetism may depend also on different kinds of strain or wave motion of this same “ether,”—either of that of space, or of the “ether” that permeates all substances. But, of course, this is all hypothesis.

So, too, of “chemical affinity,” we do not know exactly why it acts as it does, or what its force really consists in; we can only say that it depends on the different motions and appetencies or repulsions of the atoms of the various kinds of matter being made manifest, when such atoms are loosened from their previous condition by heat or what not, and so being rendered free, are able, through their inherent qualities and attractions, to arrange themselves afresh under the new conditions, in the order compelled by such endowed qualities and attractions.

We can only judge of motion, or force, or energy by witnessing its effects; and when we say that gunpowder or coal contain in them a store of potential energy, we only know that they do contain the capacity for producing movement and doing work. The gunpowder will, if inflamed, expand suddenly by the production of gases resulting from chemical changes induced by heat, and in such explosion will give liberty to enormous force.

And so likewise as to coal: on being subjected to chemical change by heat, it will, though in a less rapid way, give off its equivalent of force or energy; but as to what this acting force or energy really is, we know nothing more than that it is motion—and as to what potential force is, we know nothing more than that it is the capacity for movement in store.