136 PHYSICAL SCIENCE 



XXIV 



SEVERAL explanations are given of the temperature 

 of water. Sometimes it is hot, sometimes it boils 

 so fiercely that it cannot be used until it has given 

 off its steam in the open, or is tempered by 

 mixing cold water with it. Empedocles is of 

 opinion that as there are fires concealed in many 

 places beneath the earth, water is heated when they 

 happen to lie beneath the ground through which it 

 has to flow. Let me use an illustration. We are in 

 the habit of constructing serpentines, 1 and cylinders, 

 and vessels of several other designs in which thin 

 copper pipes are laid in descending spiral coils. The 

 object is to make the water meet the same fire over 

 and over again, and flow through a space sufficient for 

 heating it up ; so, entering as cold it comes out hot. 

 Empedocles supposes something of the same kind 

 to take place underground. People who have their 

 baths heated without fire may well believe that he 

 is right. In this case air from the heated furnace 

 is introduced. The air glides along the passages, 

 warming up the walls and vessels of the bathroom 

 just as if fire had been directly applied. In short, 

 all the cold water in these instances is changed into 

 hot by merely passing through a heated medium ; 

 and inasmuch as it is conveyed in an enclosure 

 there is no evaporation to impart a flavour to it. 2 

 Others, again, suppose that the water contracts heat 

 by issuing from or passing through ground charged 

 with sulphur ; the heat is imparted by the properties 



1 The technical name is "worm." 

 2 There is considerable doubt regarding the correct text and meaning. 



