ance of less active matter. Such heat is therefore the natural activity of the loosened particles of condensed gas and vapor. The red glow of the coal is from the beginning of that activity. The flame is the partly decomposed matter wherein the particles are in a high state of disengagement, but not wholly freed. The radiated heat is the loosened particles having assumed their natural activity, or their activity communicated to proximate substances. The heat is not a novel substance let loose from the coal, nor is it a force acting apart from substance; but it is simply the natural activity of the loosened particles of the component gases and vapors, or the transfer of that activity to the molecules of the atmosphere.
Iron is white hot from the extended swing of its component particles, which occurs as the attraction between its atoms is overcome. When heated until it becomes a fluid, the tendency of the atoms to assume their natural activity is equalized by atomicity. Under a still increased heat the tendency of the atoms to assume their natural activity exceeds atomicity, and they pass of! in a gaseous form.
Heat derived by chemical combinations is explainable according to the same principle. One substance so acts upon another as to over-
