molecule. The smallest possible unit of existence of any substance.

n. The ultimate, indivisible unit of matter. It is distinguished from the corpuscle, also the ultimate, indivisible unit of matter, by a closer resemblance to the atom, also the ultimate, indivisible unit of matter. Three great scientific theories of the structure of the universe are the molecular, the corpuscular and the atomic. A fourth affirms, with Haeckel, the condensation of precipitation of matter from ether—whose existence is proved by the condensation of precipitation. The present trend of scientific thought is toward the theory of ions. The ion differs from the molecule, the corpuscle and the atom in that it is an ion. A fifth theory is held by idiots, but it is doubtful if they know any more about the matter than the others.

. The smallest particle of matter that can exist alone. It is made up of atoms, but an atom can never exist alone, but only, with one or two possible exceptions, combined with one or more other atoms as a molecule. The molecules under present conditions are not in constant contact with each other, but are perpetually vibrating through paths, in solids probably in defined paths, in liquids and gases in perpetually new paths. The molecules collide with each other and rebound. This motion is the kinetic motion termed heat. At the absolute zero--minus 273.72° C. (-460.7° F.) the molecules would be in contact andquiescent. In the gaseous state the molecules of most substances occupy the same volume; those of a few elements occupy one-half and of others twice the normal volume. The mean free path of the molecule of hydrogen is about 1/20,000 mm. (1/508,000 inch) (Maxwell) or twice this length (Crookes), the collisions in hydrogen are about 17,750 millions per second; the diameter is about 8/10,000,000 mm. (8/254,000,000 inch) ; A particle of matter 1/4,000 mm. (1/102,000 inch) contains, it is supposed, about 40,000 molecules. The results of different authorities vary so widely as to deprive the subject of much of its interest. A Sprengel pump, such as used for exhausting Geissler tubes, or incandescent lamp bulbs, may leave only one hundred-millionth (1/100,000,000,) of an atmosphere present, giving the molecules a capability of an average free path of vibration 33 feet long.