rushes in to form new compounds; the oxygen-atom, by its impact upon the coal, has its motion of translation converted into vibratory motion, which immediately appears as heat. The clash of these atoms makes up the sum total of the energies of the combustion. The actual amount of dynamical energy set free by the union of this pound of charcoal with atmospheric oxygen is equivalent to the mechanical raising of eleven and a quarter million pounds one foot high. Let us further consider the dynamical forces inherent in the molecules of free gases, and look to a molecular explanation of the three states of matter, the solid, fluid, and gaseous. In solids the atoms are held together with a rigidity that develops the full strength of cohesive force. In liquids the same attraction is so far lessened that a definite form can only be preserved in a limited degree, as in drops of water maintaining a spheroidal, shape against the force of gravity. In the gaseous form atoms do not cohere, the cohesive force having been translated into the energy of motion, and it is this energy of motion which constitutes the expansive force of confined gases.
Suppose we have a vessel containing eight pounds of oxygen and one pound of hydrogen. This mechanical mixture of gases, invisible though it be, and harmless as it appears, is the theatre of energies wholly beyond our conceptions. Figure to your imagination these gases made up of atoms so small that a billion times a billion would scarcely fill a cubic inch, and all these atoms vibrating among themselves without actual contact. Although the minute distances over which these atoms travel are utterly immeasurable by direct appliances, we shall presently see that the energies evolved by the clash of their chemical union is something prodigious. The concussion of atoms at the union of eight pounds of oxygen with one pound of hydrogen sets free an amount of energy, in the form of heat, equivalent in mechanical value to 47,246,400 pounds let fall one foot, or the crash of a ton's weight as an avalanche down a precipice of 23,623 feet.
The three states of matter have been likened to three planes, of which the gaseous is the uppermost, the fluid occupying the intermediate plane, and the solid state for the lower one. The clash of atoms at the union of the two gases has resulted in the liberation of the energy above mentioned, but a change of state has taken place, and we now have water in the vaporous condition occupying the intermediate plane. This nine pounds of steam in condensing to water sets free an energy, the mechanical equivalent of 6,722,000 pounds let fall through the space of one foot. The next change takes us past the reduction of the temperature of the water from the boiling to the freezing point, setting free both the specific and latent heat of the water. This final fall to the plane of congelation occasions a further dissipation of energy equivalent to 2,237,256 foot-pounds, making a grand total of 56,000,000 foot pounds as the measure of energy in our nine pounds of invisible gas.
The verity of these statements might be questioned were it not that
