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CHAPTER V.

Table of Contents

THE SPECIES OF ENERGY.

Energies may be most conveniently divided on the same principle as Forces, according to the nature of the particles of bodies in which they initiate or accelerate separative motion, and resist or retard aggregative motion. But owing to the existence of two modes of Energy, the Potential and the Kinetic, whose peculiarities will form the subject of our next chapter, it will not be possible to assign a single definite name to each species, as was the case with the various Forces. It must suffice for the present to quote a few well-known instances of each.

The energies which separate Masses and resist the aggregation of Masses may be summed up under the title of Molar Energies.[5] Of Molar Energies employed in actual separation, a familiar instance is given in our own persons, when we lift a weight from the ground or carry ourselves to the top of a hill, thereby counteracting the Molar Force of gravitation by raising a body to a greater distance than before from the centre of the earth’s attraction. Another instance is seen in a cannon ball fired vertically, or a stone lifted by a crane. On a larger scale, any fresh Energy employed in removing the moon further from the earth or a planet from the sun would be a Molar Energy. Any Mass thus separated from another attracting Mass is said in the current language of physics to possess Visible Energy of Position, a term which we shall examine and endeavour to amend hereafter. Of Molar Energies employed in resistance to aggregation the most familiar instance is that of orbital movement. The moon is prevented by this Energy from aggregating with the earth, and the planets with the sun, as they would otherwise do under the influence of Molar Force or gravitation. On a smaller scale, the Energy of a bird in flying or a cannon ball fired horizontally is largely employed in counteracting gravitation. It is seldom, however, that we see Energy thus employed, except in the case of the heavenly bodies, because the Molar Force exerted by the earth in its immediate vicinity is so strong as to overcome ordinary Energies after a very short period of dissipation. Masses of the sort here described are said in the current phraseology to possess Energy of Visible Motion, which expression, like the former one, will receive attention at a later point.

The Energies which separate Molecules and resist the aggregation of Molecules may be summed up under the title of Molecular Energies. Of Molecular Energies employed in separation we have a common instance in heat, which draws apart the Molecules of a red-hot poker or a mass of boiling water, in opposition to the Molecular Force of Cohesion. The contained Energy of water acts in the same manner on a lump of sugar or a mass of dry dough. Of Molecular Energies employed in resistance to aggregation, heat under its converse aspect affords us an example. The Molecules of all bodies are prevented from aggregating into their most compressed form by the presence of heat. Thus the red-hot poker only contracts so fast as it loses its Energy by radiation. The contained Energy (or ‘latent heat’) of water similarly prevents its aggregation into ice. Large masses of water before freezing part with their Energy in the visible form of heated mist.

The Energies which separate Atoms and resist the aggregation of Atoms may be summed up under the title of Chemical Energies. A caution as to the sense in which this term must be here accepted is appended below. Of Chemical Energies employed in separation we have an instance in the electrolysis of water. The Energy disengaged by the union of elements in the battery is used up in producing chemical separation between the atoms of the electrolyte. Light produces a similar effect upon carbonic anhydride and water in the leaves of plants. Any Energy which separates a compound body into simpler or elementary bodies may be regarded as a Chemical Energy in the sense here intended. Of Chemical Energies employed in resistance to aggregation, no unequivocal instance can be cited at our present stage, though this apparent anomaly will be cleared up as we proceed. For the time the reader must be content to accept as an instance the fact that many Atoms will not combine with one another at a certain high temperature: the same temperature, in fact, at which they are driven off from their combination when actual. It will be noticed that, for the sake of uniformity, a somewhat new sense has here been given to the term ‘Chemical Energy.’ As ordinarily used at present, that term refers to the strength of the tendency which a body shows to unite with other bodies. It will be seen in the sequel that this is really a property depending upon separation and chemical nature: just as a body in proportion to its height and mass shows a tendency to aggregate with the earth: but, meanwhile, it is necessary to impose a new sense upon the term, in keeping with the analogous term ‘Chemical Affinity,’ which we have applied to the Force that aggregates Atoms.

The Energies which separate Electrical Units and resist the aggregation of Electrical Units may be summed up under the title of Electrical Energies. As in the case of Electrical Forces, our treatment of this department must be considered purely temporary and symbolical. Of Electrical Energies employed in separation we have an instance in the electrical machine, where friction produces a disunion of the Positive and Negative Units. Similarly in the torpedo and gymnotus. Of Electrical Energies employed in resisting aggregation there is again no unequivocal instance. The illustration of this deficiency must be left to later chapters.

Throughout, both in the case of Forces and Energies, it will be noticed that the same Power which initiates and accelerates one kind of motion equally resists and retards the other kind of motion. Thus, Gravitation both initiates movements of masses towards centres of attraction, and resists movements of masses away from centres of attraction. Cohesion both draws molecules together, and resists the separation of molecules: while heat draws molecules apart and resists the aggregation of molecules. So that these two Powers, the aggregative and the separative, are incessantly opposing and antagonising one another in all bodies, great or small. The amount of aggregation reached by any system of bodies at any point of time depends upon the relative proportions of its Forces and its Energies at that moment.

A table is scarcely needed for the contents of this chapter; yet for the sake of symmetry one is here appended.

Forces or Aggregative Powers.
Molar	Molecular	Atomic	Electric
Molar Energy	Molecular Energy	Chemical Energy	Electrical Energy