Not without difficulty do men perceive that there is nothing inconsistent between invariable law and endlessly varying phenomena, and that it is a more noble view of the government of this world to impute its order to a penetrating primitive wisdom, which could foresee consequences throughout a future eternity, and provide for them in the original plan at the outset, than to invoke the perpetual intervention of an ever-acting spiritual agency for the purpose of warding off misfortunes that might happen, and setting things to rights. Chemistry furnishes us with a striking example--an example very opportune in the case we are considering--of the doctrine of Diogenes of Apollonia, that the air is actually a spiritual being; for, on the discovery of several of the gases by the earlier experimenters, they were not only regarded as of a spiritual nature, but actually received the name under which they pass to this day, gheist or gas, from a belief that they were ghosts. If a labourer descended into a well and was suffocated, as if struck dead by some invisible hand; if a lamp lowered down burnt for a few moments with a lurid flame, and was then extinguished; if, in a coal mine, when the unwary workman exposed a light, on a sudden the place was filled with flashing flames and thundering explosions, tearing down the rocks and destroying every living thing in the way, often, too, without leaving on the dead any marks of violence; what better explanation could be given of such catastrophes than to impute them to some supernatural agent? Nor was there any want, in those times, of well-authenticated stories of unearthly faces and forms seen in such solitudes.
The modification made by Diogenes in the theory of Anaximenes, by converting it from a physical into a psychological system, is important, as marking the beginning of the special philosophy of Greece. The investigation of the intellectual development of the universe led the Greeks to the study of the intellect itself. In his special doctrine, Diogenes imputed the changeability of the air to its mobility; a property in which he thought it excelled all other substances, because it is among the rarest or thinnest of the elements. It is, however, said by some, who are disposed to transcendentalize his doctrine, that he did not mean the common atmospheric air, but something more attenuated and warm; and since, in its purest state, it constitutes the most perfect intellect, inferior degrees of reason must be owing to an increase of its density and moisture. Upon such a principle, the whole earth is animated by the breath of life; the souls of brutes, which differ from one another so much in intelligence, are only air in its various conditions of moisture and warmth. He explained the production of the world through condensation of the earth from air by cold, the warmth rising upward and forming the sun; in the stars he thought he recognized the respiratory organs of the world. From the preponderance of moist air in the constitution of brutes, he inferred that they are like the insane, incapable of thought, for thickness of the air impedes respiration, and therefore quick apprehension. From the fact that plants have no cavities wherein to receive the air, and are altogether unintelligent, he was led to the principle that the thinking power of man arises from the flowing of that substance throughout the body in the blood. He also explained the superior intelligence of men from their breathing a purer air than the beasts, which carry their nostrils near the ground. In these crude and puerile speculations we have the beginning of mental philosophy.