Works of grant allen, p.783
Works of Grant Allen, page 783
Electrical Kinetic Energy is equivalent to the relative motion of Electrical Units. It is seen in the lightning, in the discharge of a Leyden jar, and in the galvanic current.
It will doubtless seem strange to the reader to find the motion of masses, molecules, and atoms towards one another spoken of as a manifestation of Energy: but this seeming inconsistency will be explained in the succeeding chapter.
A table will clearly exhibit the relations here described, one example only of each species being cited.
Modes
Species
Potential.
Molar Potential
Energy.
Visible Energy
of Position.)
Molecular
Potential
Energy.
(Condensing
Steam.)
Atomic Potential
Energy.
(Chemical
Energy of Free
Elements.)
Electrical
Potential Energy.
(Tension.)
Kinetic.
Molar Kinetic
Energy.
(Orbital Motion.)
Molecular
Kinetic Energy.
(Heat.)
Atomic Kinetic
Energy.
(Chemical
Energy in Act
of Combining.)
Electrical
Kinetic Energy
(Galvanic Current.)
CHAPTER VII.
THE KINDS OF KINESIS.
Motion has three Kinds, considered from our present standpoint. It may be separative, or it may be aggregative, or it may be continuous and neutral. Each species of Kinetic Energy has a form of each Kind.
Molar motion may be separative, as when a cannon ball is shot up into the air; or aggregative, as when the same cannon ball falls to the earth; or continuous and neutral, as when a top spins in the same place.
Molecular motion may be separative, as in tearing asunder a mass; or aggregative, as in condensing steam; or continuous and neutral, as in the case of heat.
Atomic motion may be separative, as in decomposition; or aggregative, as in the act of combining. The continuous and neutral stage is not at present known, though there is reason to think that it exists.
Electrical motion may be separative, as when the Positive and Negative Electricities are divided: or aggregative, as when they are uniting. The continuous stage is possibly given us in the current which is supposed to circle round a magnet.
It was noticed in the last chapter that there was an appearance of contradiction in the statement that aggregative motions were yet manifestations of Energy. That difficulty must now be met.
When a cannon ball is shot up into the air, the motion is obviously separative, and there can be no doubt of its being a manifestation of Energy. Similarly, when a set of molecules are separated by mechanical Power or by heat, when a chemical compound is broken up into its elements, and when the Positive and Negative Electricities are sundered from one another, the separative nature of the process is obvious. We can have no hesitation in assigning each of these cases to the action of an Energy.
But when we look at the continuous and neutral motions, their character as Energies is less obvious. A moment’s consideration, however, will make it clear. The orbital motion of the planets is a continuous Energy which prevents them from aggregating with the sun as they would otherwise do. The motion of the top in like manner prevents it from falling on to the earth. The continuous vibratory molecular motion (or heat) of the red-hot poker prevents the steam or the water particles from aggregating into their cooled or liquid or solid states respectively. In short, whenever a body or molecule in a free state does not aggregate immediately with the other bodies or molecules which attract it, it is kept apart from them in virtue of some continuous or neutral movement. So soon as it parts with its Energy (or motion), it aggregates with the attracting body. Thus when the steam loses its heat it condenses into water; when the water in turn is deprived of heat, it freezes into ice; when the poker cools, it contracts; when the top parts with its motion to the air on the surface, it falls; and we have no reason to doubt that when the planets have dissipated their Energy of orbital movement by ethereal friction they will fall into the sun. This general principle — that free bodies can only be kept from aggregating by a continuous movement — is one of great importance, whose value will be seen hereafter. A body in such a state of continuous movement, which prevents it from aggregating with another, is said to be in equilibrium mobile.
When, however, we come to the aggregative motions, it would seem at first sight as though these must be classed with Forces, not with Energies. A considerable faculty of abstract thought is required to grasp their real relations: nevertheless we must endeavour to solve the problem. In doing so, we must trench a little on the subject-matter of future chapters, but only by alluding to facts already familiar to the reader. When the cannon ball reaches its highest point it possesses Potential Energy. But it does not remain suspended in the air. There are only two conditions under which it could do so, in opposition to the Force of gravitation: the first is if it is supported by a ledge or rope, in which case cohesion balances gravitation; the second is if it possesses continuous kinetic energy, in which case it would circle round the earth as a satellite until its energy was dissipated. Practically, the existence of the atmosphere makes the second case purely imaginary within the limits of that medium, though it is exhibited in the ether by such a body as the moon. As the cannon ball does not fulfil either of these conditions, it begins at once to fall. But the Potential Energy which it possesses becomes thereupon Kinetic, from moment to moment, until, at the instant of touching the earth, it has all assumed that mode. Now, we know that it does not then utterly disappear. The great principle of the Conservation of Energy teaches us that it is changed into the form of heat. Accordingly, while the two masses aggregate, certain molecules of each are separated by heat. At the moment of contact, all the motion of the fall, or Aggregative Molar Kinetic Energy, is changed into heat (or separative Molecular Kinetic Energy). There is just as much separation at last as at first: only when the ball was at its height, the separation was molar; and when the ball has touched the earth, the separation is molecular. The formula which tells us how many heat-units are generated by the fall of such and such a mass through so many feet, is a formula for the equivalence of molar separation with molecular separation. But in the intermediate time, during the fall, Potential Energy was disappearing every moment, and motion was taking its place. Though this motion was aggregative, yet, when the ground was reached, it changed into the separation of heat. Accordingly, we are justified in regarding it as essentially a transitory form of separative Power. This will be still clearer if we take such a case as the moon’s. That satellite, though attracted by the earth, is yet prevented from aggregating by its orbital movement. It possesses Potential Energy in virtue of its separation, but this does not assume the aggregative Kinetic form on account of the continuous orbital Energy. If, however, we suppose the moon to have lost its orbital movement, still retaining its present position and size, it would at once yield to the earth’s attraction, and all its Potential Energy would become Kinetic. When it reached the earth, the shock of its fall would reduce it to a very heated state, and an immense increase in size would result from the separation of its particles. The merely transferential nature of the aggregative motion is here clearly seen. So too, in the case of molecules. The Potential Energy of steam is given up when it condenses into water; and the Potential Energy of water when it forms into ice. Similarly with atoms. When oxygen unites with carbon and hydrogen in a candle, their Energy is yielded up in the form of heat, which produces a separation (or rarefaction) in the neighbouring atoms of the atmosphere. The same truth is shown in the heat and light evolved during the aggregation of Positive and Negative Electricities. Throughout we see that aggregative Energy is merely Potential Energy in the course of transformation to another form. While the really aggregative Power of Force is causing these bodies to combine, the Energy of their motion represents for a while their original separateness, and is finally transformed into a similar separateness between other bodies.
A concrete instance will make this clearer. Let us suppose the case of a pulley, with a weight at each end, one suspended in the air at the utmost height of the pulley, and the other slightly lighter, on the ground. The heavier weight possesses Potential Energy in virtue of its elevation; but, if it is free to act, it is drawn down by the aggregative Force of gravitation. In this case, however, all its Energy does not assume the Kinetic Mode as it drops: the greater part of it is used up in elevating the lighter weight to the same height, while the remainder chiefly goes off in the form of friction — that is, heat — that is, molecular separation. There is thus a mere fraction left to be converted into heat when the weight touches the ground; the mass of the Energy still remains Potential in the lighter weight. Here we see that the Energy of a falling body does not consist in its mere downward movement, but rather in that accelerating motion which is capable of being transformed into heat when the masses aggregate. If the motion be infinitely slow, the amount of heat evolved will be infinitesimal. So that the Energy of Kinesis is seen to be a mere transferential mode from one kind of separation to another. Again, we may look at the similar instance of a clock, driven by a weight. Here the weight possesses Potential Energy, in the same way as in the case of the pulley; but it has opposed to it, not another weight (that is, gravitation), but friction (that is, cohesion). As gravitation pulls down the weight through each inch of its course, the Potential Energy so lost assumes the form of heat, or separative Molecular Motion, in the wheels and bearings. When the weight reaches the ground, its Energy has all been used up, and the aggregative movement has been a real display of Force.
Thus all the kinds of motion are ultimately shown to be forms of Energy or Separative Power.
Kinetic Energies.
Separative
Separative
Molar Motion.
(In a body
raised from
the earth’s
surface.)
Separative
Molecular
Motion.
(In a body
torn apart.)
Separative
Atomic
Motion.
(In chemical
decomposition.)
Separative
Electrical
Motion.
(In electrical
machine.)
Aggregative
Aggregative
Molar Motion.
(In a falling
body.)
Aggregative
Molecular
Motion.
(In a body
cooling.)
Aggregative
Atomic
Motion.
(In a chemical
combination.)
Aggregative
Electrical
Motion.
(In lightning.)
Continuous
Continuous
Molar Motion.
(In a top or a
planet.)
Continuous
Molecular
Motion.
(In heat.)
Continuous
Atomic
Motion.
(Unknown.)
Continuous
Electrical
Motion.
(In magnet?)
CHAPTER VIII.
THE PERSISTENCE OF FORCE.
Every particle of matter has inherent in it certain Forces of which it can never be deprived. The total amount of Force or Aggregative Power in the universe is thus always a fixed quantity. This principle may be known as the Persistence of Force. It must be carefully distinguished from the opposite principle of the Conservation of Energy, to which the same name has been frequently but most incorrectly applied.
Every mass tends always to attract every other mass, and cannot be deprived of this tendency. The tendency may be masked for awhile by the intervention of other masses, as when a loose stone stands on the top of a wall, or by the presence of an Energy, as when the moon circles round the earth, or a ball is shot from a cannon; but it cannot be got rid of: for as soon as the stone topples over with the wind it falls to the ground at once; as soon as the ball parts with its Energy it similarly falls; and as soon as the moon has got rid of her motion by ethereal friction, she will aggregate with the earth.
Similarly with molecules, atoms, and electrical units: every one of them when in a free state, unrestrained by interfering Forces, and unacted upon by Separating Energies, rushes at once into a state of aggregation with its fellows.
It is important to notice that Force, unlike Energy, is inherent and indefeasible in every unit of matter. It may be counteracted for awhile by an Energy, but it still remains ready to act so soon as the Energy is dissipated; it never passes from one unit to another, as we shall see that Energy does. Force, or aggregative Power, is the primary and indefeasible attribute of every material particle.
CHAPTER IX.
THE CONSERVATION OF ENERGY.
The total amount of Energy, Potential and Kinetic, existing in the universe is always a fixed quantity. It is not, however, like Force, rigidly bound up with the individual particles in which it is from time to time manifested. As we have already seen, it can be transferred from one particle or set of particles to another. For this reason it has been deemed desirable to embody the principle in different language from that which we employed in the somewhat analogous case of Force. While Forces persist, Energies are conserved. The concrete and practical results of this difference are enormous.
It does not come within the scope of the present work to give a full account of the quantitative relations subsisting between the various species of Energy; it will be sufficient to trace their equivalence in its broader qualitative aspect. For this purpose we may consider the phenomena of Conservation under three heads: the passage of Energy from the Potential Mode to the Kinetic, the passage of Energy from the Kinetic Mode to the Potential, and the passage of Energy from one species of the Kinetic Mode to another.
Potential Energy or relative statical separation has a tendency constantly to pass into the Kinetic Mode, under the influence of Force. Every free body or particle, unless restrained by an antagonistic Force, or kept in separation by a continuous Kinetic Energy, is aggregated at once with other bodies or particles which attract it. A mass poised on a ledge or suspended by a rope is prevented from aggregating with the earth by the Force of cohesion; but when some external Energy has pushed it off the ledge or severed the rope, its Potential Energy passes at once into the Kinetic Mode, under the influence of gravitation. Two molecules of water vapour are prevented from aggregating under the relatively feeble attraction of cohesion at a distance by their inertia — that is, by the relatively strong cohesion of surrounding or intervening matters (just as a mass on the table, though attracted by the earth, is prevented from aggregating by the intervention of the cohering boards) — but when some external Energy brings them within such a distance of one another that the resistances are overcome by their mutual attractions, their Potential Energy becomes Kinetic, and they aggregate with one another. Two atoms (having affinities for one another) are similarly prevented from aggregating by inertia; but when brought within the sphere of their mutual attraction, their Potential Energy becomes at once Kinetic, and they combine with one another. So also, two electrical units are prevented from aggregating in the Leyden jar by the electrical neutrality of the glass partition; but when a conducting medium is made to connect them, their Potential Energy passes into the Kinetic Mode and they rush together at once.
Kinetic Energy or motion often passes into the Potential Mode. The Kinetic Energy of actual separation always exhibits this interchange. A cannon ball fired in the air, the piston of a steam-engine forced up by the expansive Energy of the steam, a weight hauled by a pulley to a height, a man who has climbed a mountain, are all of them instances where Molar Kinetic Energy has become Potential. The liquid condition of water melted from ice, the diffused state of vapour raised from water, are instances where Molecular Kinetic Energy has become Potential. The free hydrogen and oxygen of an electrolytic bottle, the iron and oxygen driven from their combination by heat, are instances where Atomic Kinetic Energy has become Potential. The negative and positive electricities of a Leyden jar, of a thunder-cloud and the earth, of the knobs of an electrical machine, are instances where Electrical Kinetic Energy has become Potential.
Finally, Kinetic Energy often passes from one of its species to another. Molar motion passes into Molecular motion whenever one mass interferes with the motion of another. This is true whether the motion is aggregative, or separative, or continuous. If a cannon ball be allowed to fall to the earth from a position of Potential Energy, all the Kinetic Energy which the mass acquires in its fall passes to the molecular species when it touches the ground. If it be fired into the air, and immediately checked by an iron target, the same result occurs. And if a top be stopped in spinning or the moon checked in her course, exactly like effects are or would be produced. Molecular motion passes into molar motion whenever the free separation of the moving molecules is interfered with by the cohesion of enclosing masses. Thus the steam in a cylinder pushes up the piston by its expansion; the freed nitrogen in a discharge of gunpowder in like manner pushes out the ball; and the energetic movement of a heated gas bursts the vessel within which it is confined. Molecular motion also passes into atomic motion in decomposition by heat, and into electrical motion in the friction machine. Atomic motion passes into molecular motion when heat is generated by chemical combination. It also passes (apparently) into electrical motion in the galvanic current. Electrical motion passes into molecular motion when an interrupted current produces heat. Light, which is a phenomenon connected with the ethereal medium, must be neglected for the present.
