The heat communication is then chiefly in the quarter vibration just preceding greatest rarefaction, and the vibration is not maintained.
Like Anaximenes, he believed air to be the one source of all being, and all other substances to be derived from it by condensation and rarefaction.
The doctrine of Anaximenes, who unites the conceptions of a determinate and indeterminate original substance adopted by Thales and Anaximander in the hypothesis of a primordial and all-generating air, is a clear advance on these theories, inasmuch as it introduces the scientific idea of condensation and rarefaction as the great generating or transforming agencies.
Thus Thales recognized change, but was not careful to explain it; Anaximander attributed to change two directions; Anaximenes conceived the two sorts of change as rarefaction and condensation; Heraclitus, perceiving that, if, as his predecessors had tacitly assumed, change was occasional, the interference of a moving cause was necessary, made change perpetual.
Such a circulation of air can only be effected by mechanical means when the workings are of any extent, the methods actually adopted being - (i) The rarefaction of the air in the upcast pit by a furnace placed at the bottom; and (2) Exhaustion by machinery at the surface.
