Is cold the mere privation of heat? 309. This is denied, for cold seems to act on fluids and on solids: like heat or other actual substances, it has a productive power, 310. Further, a mere privation is not capable of degrees; but cold exists in different degrees, 310. A privation is nothing; cold is something, 311. A privation is not the object of any of our senses; but cold can be felt, 311. Privation is something single and simple; substances have differences, continually varying; and thus it is with cold, therefore cold must be a substance, 312. Cold acts as a substance; it resists heat, and overcomes it or is vanquished by it, 312. As there are four elements, of which all things are composed, so there should be four qualities, heat and cold, drought and moisture, 313. What sort of substance is cold? 314. The air, when it becomes dark, becomes also cold, 315. The freezing of water is caused by cold air, 316. Great rivers and lakes are not frozen to the bottom, because the air does not reach so far; the power of cold is therefore as many think, from the air, 317; but this is doubtful, 318. Water makes things black; air makes them white, 318. Oil is transparent because so much air is in it, 318. It does not easily freeze, 319. Cold things are always heavy, 319. Fire and water are opposites, 320. In winter, heat is driven inward by cold, 321. It is driven downward from the surfaces of great rivers, 321. Several considerations show that water, and not air, is the cause of cold, 322. Water is cold of itself, being the opposite of fire, 323. Opinion of Chrysippus combated, 324. The earth, because it is dark, might be considered the cause of cold, 324, 325. But many hot things are dark, 326. Cold makes things hard, heavy, rigid, and capable of resistance: the earth is therefore the source of cold, 326, 327. Several considerations which seem to prove that heat exists in every thing except the earth, and that cold proceeds as a substance from the earth; which, and the whole subject, in conclusion, is left in doubt, to be decided as the reader pleases. 327-330. WHETHER WATER OR FIRE BE MOST USEFUL. BY THE SAME HAND. 1. Arguments of the superior usefulness of Water: We need it at all times and in all places; it is not so with fire. Water was given to man at his first creation; fire was introduced by Prometheus. Some men and all brute animals can live without fire, but not without water. Fire is often pernicious; water never. Fire cannot be kept up without expense; water requires no expense. Water, or the sea, is the great civilizer of man, 331-334. 2. Arguments in behalf of Fire: Heat is the exciting cause of vegetation; water becomes putrid when fire leaves it; animals perish without heat; death is only the absence of heat; water is made more useful by fire; the arts cannot exist without fire, 334-337.