8Since, therefore, all the large known rivers in the world seem to flow from the north, and towards the land of Africa, because those are in the southern regions under the sun’s course, where there is little moisture, and but few springs and rivers, it follows that those sources which are in the north and north-east, are much better than others, unless they run over a sulphureous, aluminous, or bituminous soil, for their quality is thereby changed, and whether hot or cold, their water is then of bad smell and taste. It is not that water, by its nature, is hot, but when cold, it is heated by running over a hot soil, and issues warm from the earth through the different pores: it does not, however, long remain in that state, but soon becomes cold; whereas, if it were naturally hot, it would not so soon grow cool; for it does not lose its taste, smell, and colour, which, from the purity of its nature, remain unchanged and discoloured.
8Therefore, since in descriptions of the world it appears that all rivers of any size flow from the north, and since in the plains of Africa, which are exposed to the course of the sun in the south, the moisture is deeply hidden, springs not common, and rivers rare, it follows that the sources of springs which lie to the north or northeast are much better, unless they hit upon a place which is full of sulphur, alum, or asphalt. In this case they are completely changed, and flow in springs which have a bad smell and taste, whether the water is hot or cold.
The fact is, heat is not at all a property of water, but when a stream of cold water happens upon a hot place, it boils up, and issues through the fissures and out of the ground in a state of heat. This cannot last very long, but in a short time the water becomes cold. If it were naturally hot, it would not cool off and lose its heat. Its taste, however, and its smell and colour are not restored, because it has become saturated and compounded with these qualities on account of the rarity of its nature.