certainly as a heated ball cools in the open air; nor is there any indication of any method by which this power is to be restored. '

The correlation of forces --- energies --- does not carry with it eternal evolution, but the opposite rather. Energies that are put to any work are exhausted by that work as working powers, as much as man himself, who is one expression of them. A certain condition of energies is called for before work can be done, and that condition is lost by the work that follows from it. The three chief forms of potential energy in the world are suspended bodies, heated bodies, and bodies of a high chemical composition. But the weight falls in performing labor, the heat is lost, and the chemical relation is broken up. We can not restore the height, nor the fuel, nor the food, without a fresh draft on our original resources. Every change by which work is done is thus a fresh reduction of potentialities, and looks to their ultimate exhaustion. There is no more perpetual motion in the Universe as a whole, than in any of its parts. The revolution of the Earth in its orbit, if it involves any work, any resistance less or more, must come to an end. All the changes involved in labor are from mutable to stable equilibrium. The constructive power at any one time present in the solar system is wholly a finite quantity, steadily reduced by expenditure. Potential energy passes into kinetic energy, and is then dispersed in some form of work, the ultimate escape being chiefly in the radiation of heat. When then the sun, the present reservoir of energy, shall