5. According to the theory, the original atoms during the process of world-making united into _molecules_. The laws according to which atoms unite,--so that, for instance, the hydrogen atom each unites with two atoms of oxygen, and so down the list of all known existences,--these laws are among the assured results of scientific study. Now, the entire science of chemistry in all its branches is built upon the axiom that molecules are _absolutely unalterable_ and that molecules of the same kind are always absolutely identical. A molecule of water is always and invariably composed of two atoms of hydrogen and one of oxygen. A molecule of sulphuric acid invariably contains two atoms of hydrogen, one of sulphur, and four of oxygen. A molecule of potassium chlorate is always composed of just one atom of potassium chloride and three atoms of oxygen. Never is there any variation of these proportions in the same element, and a chemist will, without handling the elements, merely by mathematical calculation, unerringly produce new combinations, relying on the absolute constancy of the relations of atoms and molecules. Now, the theory that in the beginning of things, out of a mass of atoms diffused without form through space, molecules came into being, each kind or type composed of atoms according to a proportion peculiarly its own, cannot be accepted unless it is shown in what manner the laws came into existence according to which these combinations take place. Clerk Maxwell concludes a masterly statement of this aspect of the hypothesis by asking: "Who can restrain the ulterior question, Whence then these myriad types of the same letter imprinted on the earth, the sun, the stars, as if the very mould used here had been lent to Sirius, and passed on through the constellations? No theory of evolution can be formed to account for the similarity of the molecules throughout all time, and throughout the whole region of the stellar universe; for evolution necessarily implies continuous change, and the molecule (as known to science) is incapable of growth or decay, of generation or destruction." The Origin of Life.