Man has to deal with three great categories of phenomena--the inorganic, the organic, and the psychic. In the inorganic, chemistry first and then physics have given us a picture whose broad outlines are now familiar. There is but one type and store of energy in Nature, whether it drives a train, animates a man, radiates in heat or light, inheres in a falling stone. There is but one substance. All bodies of trees, of men, rivers and rocks, the clouds in the air and the air itself, precious stones and common clay--all can be resolved into a limited number of elements. And these elements in their turn can be resolved into combinations, differing, it appears, only quantitatively from each other, of electrical charges; so that at the last all matter is one, and becomes perhaps indistinguishable, or at least inseparable, from energy. There is no personal operator for particular happenings; the lightning and the volcano are the inevitable outcome of the material constitution of things, equally with the form and colour of a pebble and with the fact that it will drop to the ground if it is let fall. All is impersonal order and unity. There is, however, one other great fact about the system of inorganic matter. The energy contained in it tends to be degraded, as the physicists say--in other words to become less readily available. There is available energy in moving matter. There is potential energy in all matter, dependent upon whether it can be set in motion. But if the sea were to cover the whole surface of the globe, it would be impossible to extract energy from running water as we do now, because no water would be running. So too heat is energy; but it is only available when it can flow, when there are hotter and colder bodies. The law under which transformations of energy operate has now been investigated, and it has been established that in every energy-transaction a certain modicum goes to waste as unavailable heat, so that, unless some at present unforeseen change occurs, the last state of the universe, considered as a purely physico-chemical mechanism, will be one of death, of inactivity, with all matter at a uniform low temperature and the whole stock of energy locked up and unavailable in this sea of tranquillity. True for one thing that an almost inconceivable number of millions of years must elapse before this “death of matter” is realized; and for another that we are unable to understand how such a progressive degradation could have been in operation from all eternity. We must not expect complete knowledge within a few years or a few centuries; but even if the beginning is veiled--for there is no more evidence for a “creation” than for (say) a rhythmic reversal of the direction of energy-availability--and if it is always possible that some unforeseen change in the process should occur before the whole runs down, yet it is a fact (and we are resolved to be agnostic save about facts)