Tested from a view-point outside the onlooker-consciousness, this whole picture of the interaction between matter and heat appears to run counter to the cosmic order of things in a way typical of other spectator-theories. Ancient man, if confronted with this picture, would have said that it means explaining the element Fire by the quality Cold. For each of those minute particles, in its solidity and state of spatial separation from the others, represents an effigy of the earth and thereby the element Earth itself. He would be unable to understand why phenomena of the 'warm' element Fire should be explained by its very opposite. Moreover, Fire forms part of the ever 'youthful' realm of the world, whereas anything which exists as a spatially discernible entity, capable of being moved about mechanically, must have grown cosmically 'old'.
That Ruskin was as much on the alert in regard to this theory as he was in regard to Newton's theory of gravitation, is shown by the following utterance from his The Queen of the Air. Obviously stirred by Tyndall's newly published treatise, Heat as a Mode of Motion, Ruskin felt the need to criticize the endeavour of contemporary science 'to simplify the various forms of energy more and more into modes of one force, or finally into mere motion, communicable in various states, but not destructible', by declaring that he would himself 'like better in order of thought3 to consider motion as a mode of heat than heat as a mode of motion'.
These words of Ruskin touch also on the law of conservation of energy, of which we said that it also called for a preliminary examination. What we now have to find out is the factual basis on which this law rests.
*
The conception of the law of conservation of energy arose from the discovery of the constant numerical relation between heat and mechanical work, known as the mechanical equivalent of heat. This discovery was made at about the same time by Joule in England and J. R. Mayer in Germany, although by entirely different routes. Joule, a brewer, was a man of practical bent. Trained by Dalton, the founder of the atomic theory, in experimental research, he continued Rumford's and Davy's researches which they had undertaken to prove that heat is not, as it was for a time believed to be, a ponderable substance, but an imponderable agent. As a starting-point he took the heating effect of electric currents. The fact that these could be generated by turning a machine, that is, by the expenditure of mechanical energy, gave him the idea of determining the amount of work done by the machine and then comparing this with the amount of heat generated by the current. A number of ingenious experiments enabled him to determine with increasing exactitude the numerical relation between work and heat, as well as to establish the absolute constancy of the relation.
This he regarded as proof of the mechanical theory of heat, which he had taken from Rumford and Davy. What simpler explanation could there be for the constant numerical relation between work and heat than the conception that transformation of one form of energy into another was simply a transmission of motion from one object to another? From the quantitative equality of expended and generated energy was it not natural to argue the qualitative similarity of the two forms of energy, which only externally seemed different?
It was by quite a different path that the Heilbronn doctor, Mayer, arrived at his results. To escape from the narrowness of his South German home town, he went, while still a youth, as doctor to a Dutch ship sailing to Java. When in the tropics he treated a number of sailors by blood-letting, he observed that the venous blood was much nearer in colour to the paler arterial blood than was usual at home. This change in the colour he attributed to the diminished intensity of bodily combustion, due, he believed, to the higher temperature of the tropics.
Scarcely had this thought passed through his mind than it induced another - that of a universal interrelationship between all possible forms of energy. This last idea so took possession of him that during the return voyage, as he himself related, he could scarcely think of anything but how to prove the correctness of his idea and what the consequences would be for the general view of nature. From the moment of his return he devoted his life to practical research into the connexion between the various manifestations of energy. It was in this way that he was led to the determination of the so-called mechanical equivalent of heat, shortly before the same discovery was made in a quite different manner by Joule.
If one considers how slender a connexion there was between Mayer's observation on the sailors in Java and the idea of the quantitative equilibrium of all physical nature-forces, and if one contrasts this with the fanaticism he showed during the rest of his life in proving against all obstacles the correctness of his idea, one must feel that the origin of the thought in Mayer's mind lay elsewhere than in mere physical observations and logical deductions. Confirmation of this may be found in what Mayer himself declared to be his view concerning the actual grounds for the existence of a constant numerical association between the various manifestations of natural energy.
So far as science allowed Mayer any credit for his work, this was based on the opinion that through his discovery he had provided the final vindication of the mechanical theory of heat. This judgment, however, was only piling one wrong upon another. Mayer's destiny was truly tragic. When he began to publicize his conviction of the numerical equilibrium between spent and created energy, he met with so much scepticism, even derision, that from sheer despair his mind at times became clouded. When at last toward the end of his life he received the recognition his discovery deserved (not before being dragged through a painful priority dispute which Joule forced upon him and lost), the scientists had begun to use his idea for bolstering up a hypothesis directly counter to the idea which had led him to his discovery, and for the sake of which he had accepted so much suffering.