We should obtain a wholly wrong impression of what Bishop Berkeley calls 'the philosophy of fire' if we set before our minds in this connection, the raging element whose strength is in destruction. Let us rather picture to ourselves as the type of fire the benign and beatific solar heat, the quickener and fosterer of all terrestrial life. For according to Zeno, there were two kinds of fire, the one destructive, the other what we may call 'constructive,' and which he called 'artistic'. This latter kind of fire, which was known as aether, was the substance of the heavenly bodies, as it was also of the soul of animals and of the 'nature' of plants. Chrysippus, following Heraclitus, taught that the elements passed into one another by a process of condensation and rarefaction. Fire first became solidified into air, then air into water and lastly water into earth. The process of dissolution took place in the reverse order, earth being rarefied into water, water into air, and air into fire. It is allowable to see in this old world doctrine an anticipation of the modern idea of different states of matter--the solid, the liquid, and the gaseous, with a fourth beyond the gaseous which science can still only guess at, and in which matter seems almost to merge into spirit. Each of the four elements had its own abode in the universe. Outermost of all was the ethereal 'fire' which was divided into two spheres: first that of the fixed stars and next that of the planets. Below this lay the sphere of 'air', below this again that of 'water', and lowest or in other words, most central of all was the sphere of 'earth', the solid foundation of the whole structure. Water might be said to be above earth because nowhere was there water to be found without earth beneath it, but the surface of water was always equidistant from the centre, whereas earth had prominences which rose above water. When we say that the Stoics regarded the universe as a plenum, the reader must understand by 'the universe' the Cosmos or ordered whole. Within this there was no emptiness owing to the pressure of the celestial upon the terrestrial sphere. But outside of this lay the infinite void without beginning, middle, or end. This occupied a very ambiguous position In their scheme. It was not being, for being was confined to body and yet it was there. It was in fact nothing, and that was why it was infinite. For as nothing cannot be bound to any thing, so neither can there be any bound to nothing. But while bodiless itself, it had the capacity to contain body, a fact which enabled it, despite its non-entity, to serve, as we shall see, a useful purpose.