energy and, inferentially, of the quantivalent relations of all energies. He originated the now usual method of determining the quantivalence of heat and thermal and dynamical forms of energy by the storage of the heat of friction in a mass of water, and, by the churning of liquids, of similarly storing the heat of fluid-friction. He adopted the view that the energy developed in the animal system is the measure of a certain proportion of the stored energy of the food thus utilized. Thus he extended the principle of persistence to the organic world and to living creatures, opening the way to the final generalizations and conclusions of the enunciator of the so-called 'Law of Substance.'
Thus Rumford was the first to prove by experimental investigation the transformability of the energies, to exhibit the principle in its most important example and to derive, by physical research, the principle of the thermodynamic equivalence of energies and the fact of heat being simply a form of energy and a mode of motion of substance.
Mayer seems to have been the first to recognize a now well-understood fact: that, if we are to gain a more effective development of the energies, potential in our fuels, which are practically our only sources of commercially useful energy, we must find a way to transform the potential energy of chemical union directly into some other form than the thermal and by some other than the thermodynamic process. He says[1] that 'the evident wastes of the thermodynamic process as illustrated in our best steam engines justify us in seeking other methods of energytransformation,' more particularly by the transformation into motion of electricity obtained by chemical means.
Mayer was probably the first to write under the definite title 'The Mechanical Equivalent of Heat.'[2] He was the first to declare, in so many words: 'the vis viva of the universe is a constant quantity.'[3] He stated that 'the heat produced mechanically by the organism must bear an invariable quantitative relation to the work expended in producing it.'
This he deduced from his 'physiological theory of combustion.' He anticipates the idea of the permanence of the universe in its present general aspect by the suggestion that this redistribution of energy, 'degraded' by other phenomena, may be effected 'by the falling together of previously invisible double stars' or equivalent phenomena.[4] He finds by computation that the energy transformed through such collisions 'would considerably exceed that which an equal weight of matter could furnish by the most intense process of chemical action'—in other words: it would resolve the solid mass into its elementary atoms; which is pre-
