the most refined researches give unvarying results. Suppose we reverse this experiment, and, commencing with nine pounds of ice, we will, by a process of mental abstraction, again bring our conceptions down to the immeasurably small, and fix our attention upon the molecules of the ice. Figure to yourself the atoms of each molecule as being in oscillation through points of equilibrium. And, while your attention is centred upon the motions taking place in the interior of the mass, we will let fall upon the block of ice a concentrated beam of sunlight, and see how it deals with the inherent forces of cohesion and chemical affinity. The solar undulations impinge upon the molecules of the ice, and, under this bombardment of heat waves, see how rapidly the atoms accelerate their motions! All this while the contest is going on between the dynamic energy of the sun's waves of heat and the cohesive force of the molecules. Beautifully and symmetrically the forces of Nature built up the crystalline mass, and as silently and surely the sun's competency of heat will effect its liquefaction. Thus far we have seen the atoms accelerating in velocity by virtue of the energy imparted by the solar-heat waves, and all this time they are vibrating within the definite limits of the molecule. A further increase of heat will increase the motion of the atoms, thus tending to a rupture of the bonds of cohesive attraction. The struggle goes on until the ice melts, by which process we have solar energy conserved in the latent heat of water. The molecules being thrown almost beyond the range of cohesive force, their movements are no longer confined to their former limits, but may extend throughout the length and breadth of the mass. This is the fluid state. The amount of energy required to swing the atoms so nearly beyond the range of cohesive attraction, or simply to melt the ice, is equal to 500 tons raised one foot high. This force still exists as transmuted energy, and is the latent heat of water. A further addition of heat takes the form of increased vibratory action up to the boiling-point. Then comes another struggle seven times greater than the first. This last remnant of cohesive force of water must; be surrendered, and the heat-energy necessary to perform the act is conserved or transmuted into the latent heat of steam. The last vestige of cohesive force now being gone, the molecules of steam are free to oscillate in all directions, and impinge against the walls of the containing vessel. If we continue the application of heat to the point of dissociation, the molecules of vapor will have acquired a momentum sufficient to rupture the bonds of chemical affinity. And here the energy required to separate the molecules of steam into its constituent atoms of oxygen and hydrogen is simply prodigious, being about forty-eight times as much as was necessary for the process of liquefaction. Thus the aggregated energies required to set free the oxygen and hydrogen in our nine pounds of ice are equivalent to the raising of a ton's weight 28,000 feet, and we now have the original nine pounds of gas, laden with the potential energies of 56,000,000 foot-pounds, which is just
