In the next place we have to consider that there are divers kinds of fire. There are, for example, first, flame ; and secondly, those emanations of flame which do not burn but only give light to the eyes ; thirdly, the remains of fire, which are seen in red-hot embers after the flame has been extinguished. There are similar differences in the air ; of which the brightest part is called the aether, and the most turbid sort mist and darkness ; and there are various other nameless kinds which arise from the inequality of the triangles. Water, again, admits in the first place of a division into two kinds ; the one liquid and the other fusile. The liquid kind is composed of the small and unequal particles of water ; and moves itself and is moved by other bodies owing to the want of uniformity and the shape of its particles ; whereas the fusile kind, being formed of large and uniform particles, is more stable than the other, and is heavy and compact by reason of its uniformity. But when fire gets in and dissolves the particles and destroys the uniformity, it has greater mobility, and becoming fluid is thrust forth by the neighbouring air and spreads upon the earth ; and this dissolution of the solid masses is called melting, and their spreading out upon the earth flowing. Again, when the fire goes out of the fusile substance, it does not pass into vacuum, but into the neighbouring air ; and the air which is displaced forces together the liquid and still moveable mass into the place which was occupied by the fire, and unites it with itself. Thus compressed the mass resumes its equability, and is again at unity with itself, because the fire which was the author of the inequality has retreated ; and this departure of the fire is called cooling, and the coming together which follows upon it is termed congealment. Of all the kinds termed fusile, that which is the densest and is formed out of the finest and most uniform parts is that most precious possession called gold, which is hardened by filtration through rock ; this is unique in kind, and has both a glittering and a yellow colour. A shoot of gold, which is so dense as to be very hard, and takes a black colour, is termed adamant. There is also another kind which has parts nearly like gold, and of which there are several species ; it is denser than gold, and it contains a small and fine portion of earth, and is therefore harder, yet also lighter because of the great interstices which it has within itself ; and this substance, which is one of the bright and denser kinds of water, when solidified is called copper. There is an alloy of earth mingled with it, which, when the two parts grow old and are disunited, shows itself separately and is called rust. The remaining phenomena of the same kind there will be no difficulty in reasoning out by the method of probabilities. A man may sometimes set aside meditations about eternal things, and for recreation turn to consider the truths of generation which are probable only ; he will thus gain a pleasure not to be repented of, and secure for himself while he lives a wise and moderate pastime. Let us grant ourselves this indulgence, and go through the probabilities relating to the same subjects which follow next in order.
Water which is mingled with fire, so much as is fine and liquid (being so called by reason of its motion and the way in which it rolls along the ground), and soft, because its bases give way are less stable than those of earth, when separated from fire and air and isolated, becomes more uniform, and by their retirement is compressed into itself ; and if the condensation be very great, the water above the earth becomes hail, but on the earth, ice ; and that which is congealed in a less degree and is only half solid, when above the earth is called snow, and when upon the earth, and condensed from dew, hoarfrost. Then, again, there are the numerous kinds of water which have been mingled with one another, and are distilled through plants which grow in the earth ; and this whole class is called by the name of juices or saps. The unequal admixture of these fluids creates a variety of species ; most of them are nameless, but four which are of a fiery nature are clearly distinguished and have names. First there is wine, which warms the soul as well as the body : secondly, there is the oily nature, which is smooth and divides the visual ray, and for this reason is bright and shining and of a glistening appearance, including pitch, the juice of the castor berry, oil itself, and other things of a like kind : thirdly, there is the class of substances which expand the contracted parts of the mouth, until they return to their natural state, and by reason of this property create sweetness ; — these are included under the general name of honey : and, lastly, there is a frothy nature, which differs from all juices, having a burning quality which dissolves the flesh ; it is called opos (a vegetable acid).
As to the kinds of earth, that which is filtered through water passes into stone in the following manner : — The water which mixes with the earth and is broken up in the process changes into air, and taking this form mounts into its own place. But as there is no surrounding vacuum it thrusts away the neighbouring air, and this being rendered heavy, and, when it is displaced, having been poured around the mass of earth, forcibly compresses it and drives it into the vacant space whence the new air had come up ; and the earth when compressed by the air into an indissoluble union with water becomes rock. The fairer sort is that which is made up of equal and similar parts and is transparent ; that which has the opposite qualities is inferior. But when all the watery part is suddenly drawn out by fire, a more brittle substance is formed, to which we give the name of pottery. Sometimes also moisture may remain, and the earth which has been fused by fire becomes, when cool, a certain stone of a black colour. A like separation of the water which had been copiously mingled with them may occur in two substances composed of finer particles of earth and of a briny nature ; out of either of them a half solid body is then formed, soluble in water — the one, soda, which is used for purging away oil and earth, and other, salt, which harmonizes so well in combinations pleasing to the palate, and is, as the law testifies, a substance dear to the gods. The compounds of earth and water are not soluble by water, but by fire only, and for this reason : — Neither fire nor air melt masses of earth ; for their particles, being smaller than the interstices in its structure, have plenty of room to move without forcing their way, and so they leave the earth unmelted and undissolved ; but particles of water, which are larger, force a passage, and dissolve and melt the earth. Wherefore earth when not consolidated by force is dissolved by water only ; when consolidated, by nothing but fire ; for this is the only body which can find an entrance. The cohesion of water again, when very strong, is dissolved by fire only — when weaker, then either by air or fire — the former entering the interstices, and the latter penetrating even the triangles. But nothing can dissolve air, when strongly condensed, which does not reach the elements or triangles ; or if not strongly condensed, then only fire can dissolve it. As to bodies composed of earth and water, while the water occupies the vacant interstices of the earth in them which are compressed by force, the particles of water which approach them from without, finding no entrance, flow around the entire mass and leave it undissolved ; but the particles of fire, entering into the interstices of the water, do to the water what water does to earth and fire to air, and are the sole causes of the compound body of earth and water liquefying and becoming fluid. Now these bodies are of two kinds ; some of them, such as glass and the fusible sort of stones, have less water than they have earth ; on the other hand, substances of the nature of wax and incense have more of water entering into their composition.