21. The physicians also tell us that the nature of all sorts of earth is binding and restrictive; and they number up several sorts of metals which are made use of in physic by reason of their styptic and binding qualities. For the element of earth is fit neither to cut nor to move, neither has it any points, neither is it subject to be softened or melted, but is firm and stable like a cube; and therefore it has both ponderosity and coldness, and the faculty to thicken and condense moist things; and it causes tremblings and quiverings in bodies by reason of its inequality; and if it get the better by the utter expulsion and extinguishing of the heat, it occasions a frozen and deadly habit of body. Therefore earth either does not consume by burning, or else burns with a very slow and difficult progress. But the air many times darts forth flame from itself; and being once set on fire, it grows fluid and flashes out in lightning. Heat also feeds upon moisture; for it is not the solid part of the wood, but the moist and oily part, that is combustible; which being consumed, the solid and dry is left behind in the ashes. Neither do they arrive at their mark, who, pretending to burn the ashes also, sprinkle them with oil and grease; for when the liquid is consumed, the earthy part remains, do what they can. Therefore, because the earth is not only of a nature not to be moved from its station, but also unalterable in its substance and always abiding in the habitation of the Gods, the ancients well called it Hestia or Vesta (from _standing_), by reason of its immobility and concretion; of which cold is the bond or ligament, as Archelaus the philosopher termed it, which nothing is able to unloosen or soften, as not being capable of heat and warmth. As for those who say they have been sensible of the cold of air and water, but never felt the earth so cold, they consider only the surface of the earth, which is a mixture of air, water, sun, and heat. They are no better than people who deny the aether to be naturally and primitively hot, but believe it to be either scalding water or red hot iron, because they feel and handle the one, but are not sensible of the pure and celestial fire. In like manner, neither do they see the earth which lies concealed at the bottom, though that be what is chiefly to be taken for the earth, separated from all other things. We may see some token of this lower earth in these rocks here about us, which from their depths send forth a cold vapor so sharp and vehement that it is hard to be endured. They also that desire cool drink throw small flint stones into water. For it becomes denser and quicker to the taste, through the cold which is carried upward fresh and unmixed from the stones.