The philosophy of biology

by James Johnstone

POTENTIAL ENERGY

Therefore, if energy disappears or appears, we do not say that it is destroyed or is created: we invent potential energies, into which we suppose that the energies in question have become transformed, in order that we may still think of them as being subject to an a priori principle of conservation. Although a particle of radium continually generates heat, we do not therefore think of the first principle of energetics as being invalidated, for we suppose that the energy which thus appears was really potential in the atoms of radium. But it was contrary to all our former experience of atoms that they should contain any other energy than that of their own motion, and so the further assumption was made that the atom, at least the atom of the radio-active substance, is really complex, and not simple, as chemical theory demands. It is made up of smaller particles, and possesses a definite structure. In certain circumstances the atom may disintegrate, and the energy which held together its particles, whether these were simpler corpuscles or electrons, is given off as the heat which the radio-active substance apparently generates. The potential energy of the chemical atom is therefore a hypothesis which has been devised in order to preserve the validity of the law of conservation, and the reality of this hypothesis is being tested by investigation. If we accept it as true, are the deductions made from it justified in our experience? That is the test which must be satisfied in all the hypotheses where potential energies are invented, and the potentials are only real if the test is satisfactory. The golf ball at rest at the top of the hill is a different entity from the golf ball at rest at the bottom of the hill: it is capable of developing energy, for a touch may cause it to roll down the hill, when most of the energy which was expended in order to drive it to the top of the hill will reappear in the form of the kinetic energy of motion of the ball. The atoms of hydrogen and oxygen which were dissociated by the energy of the electric current are different things from the atoms of hydrogen and oxygen which are combined together to form the molecules of water. Their state when the gases are in the elementary condition, or are “free,” is that of molecules moving rapidly and incessantly, rebounding from each other after colliding with each other: they possess energy of position—potential energy—because they are separate from each other. If they “combine,” as when a minute electric spark explodes the mixture of gases, they tractate together, and remain in proximity to each other, becoming molecules of water. The energy which became potential in the gaseous mixture, when the electric energy of the current seemed to disappear, now appears as the heat generated by the combustion, that is, as the greatly increased kinetic energy of the molecules of the gas (steam) which takes the place of the mixture of hydrogen and oxygen. Previous to the explosion this gas was a mixture of molecules of hydrogen and oxygen (2H₂+2O) at the ordinary temperature, but after the explosion it consists of a smaller number of molecules at a very much higher temperature.

What is “energy of position”? The golf ball at the bottom of the hill was at a distance of R feet from the centre of the earth, but at the top of the hill it is at a distance of R + 100 feet from the centre of the earth. In the first case it was free to fall R feet, but in the second case it is free to fall R + 100 feet. The atoms of the constituent molecules of water occupy the position H−O−H, the bonds (−) indicating that the atoms are very close together; but when the water is decomposed by an electric current, the atoms occupy the positions O−O + H−H + H−H, the (+) indicating that the atoms are relatively far apart from each other. Now the golf ball and the earth, or the atoms of hydrogen and oxygen, are physically the same material entities, whether they are close together or far apart, yet when the earth and the ball, or the atoms of oxygen and hydrogen, are separated from each other, their “properties” are different from what they are when they are close together. What is it that makes the difference? It is that which is between them. Is it, in the last case, “the potential energy of chemical affinity”? This dreadful phrase is actually used in a recent book on biology: “In the elements carbon and oxygen, so long as they remain separate, a certain amount of energy remains latent. When the carbon and oxygen atoms are allowed to come together and unite, this potential energy of chemical affinity is liberated as kinetic energy.” What is changed by the tractation and pellation (the terms suggested by Soddy in place of the anthropomorphic ones, “attraction” and “repulsion”)? It is the ether which has become changed in some way. Potential energy resides therefore in the ether of space.