The heat communication is then chiefly in the quarter vibration just preceding greatest rarefaction, and the vibration is not maintained.
The process by which things grow is twofold, condensation (lruevwvcs) and rarefaction apaicovcs), or, in other words, heat and cold.
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.
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.
But if the heat is given at the instant of greatest rarefaction, the increase of pressure lessens the difference from the undisturbed pressure, and lessens the potential energy, so that during the return less kinetic energy is formed and the vibration tends to die away.