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.