We have already spoken of the atomic constitution of bodies. It remains now to explain the simplicity and beauty which mark every variety of combination under chemical force. As a prominent and striking example, water is a compound of two gaseous bodies, oxygen and hydrogen:-- If we decompose water by means of galvanic electricity, or determine its composition by direct chemical analysis, we shall find it consists of two volumes of hydrogen gas, united to one volume of oxygen, or, by weight, of one part of hydrogen combined with eight of oxygen. In 100 parts, therefore, we should find-- Oxygen 88·9 Hydrogen 11·0 It is found in the same way that the theoretical weight of the atom of carbon is 6, and that of nitrogen 14; whilst the atom of iron is 28, that of silver 108, of gold 199, and that of platinum and iridium each 98.[202] Now, as these are the relative weights of the ultimate indivisible atom, it follows that all combinations must be either atom to atom, or one to two, three, or four; but that in no case should combination take place in any other than a multiple proportion of the equivalent or atomic number. This is found to be the case. Oxygen, for instance, combines as one, two, or three atoms; its combination presenting some multiple of its equivalent number 8, as 16, or 24: and in like manner the combining quantity of carbon is 6, or some multiple of that number. Where this law is not found strictly to agree with analytical results, of which some examples are afforded by the sesquioxides, it may be attributed, without doubt, to some error of analysis or in the method of calculation. Nothing can be more perfect than the manner in which nature regulates the order of combination. We have no uncertain arrangement; but, however great the number of the atoms of one element may be, over those of another, those only combine which are required, according to this great natural law, to form the compound, all the others still remaining free and uncombined. These results certainly appear to prove that the elementary particles of matter are not of the same specific gravities. Do they not also indicate that any alteration in the specific gravity of the atom would give rise to a new series of compounds, thus apparently producing a new element? Surely there is nothing irrational in the idea that the influences of heat or electricity, or of other powers of which as yet we know nothing, may be sufficient to effect such changes in the atomic constituents of this earth. The combination of elementary atoms takes place under the influence of an unknown force which we are compelled to express by a figurative term, _affinity_. In some cases it would appear that the disposition of two bodies to unite, is determined by the electrical condition; but a closer examination of the question than it is possible to enter into in this place, clearly shows that some physical state, not electrical, influences combining power.