We have already noted that there was a time when fire was unknown. How then could the Paleolithic man, thrown wholly upon his own observation and resources, come upon this discovery, which was to work such changes for the future? Only from his observance of natural phenomena. When storms swept over desert and plain, vivid lightning flashed, and occasionally some tree was struck by the bolt and flamed up, greatly to the astonishment and alarm of the unknowing mind. At other times, volcanic eruptions occurred, and dry leaves and forests caught on fire from flying cinders. In the natural course of events, men soon found that the warmth of burning wood was agreeable, that fire at night allowed them to keep watch over possible invaders--whether man or wild beasts--and that the interior of a tree's trunk could be more easily removed by burning than by laborious scraping out with stone implements. Having once tasted roasted flesh, a desire for cooked food was probably developed. Such a valued possession as fire proved, needed to be carefully tended, and when it was exhausted, human ingenuity set to work to create it anew. It is not unlikely that sparks occasionally struck out from flint when it was being chipped into shape for a weapon or implement. Necessity and desire have always worked wonders, and primitive man learned shortly to produce the vital spark, both by friction and by drilling. Having mastered the art of fire-making, many innovations were consequent upon it. Some fixed habitation was necessary if the coals were to be kept covered from day to day, and from meal to meal. Cooked foods gradually took the place of raw ones; in cold weather the family grew to gather around the fire, where meals were prepared and warmth was to be found. When the family, clan or tribe removed to a new home, coals were carried to kindle the fire upon the new hearth. When men journeyed abroad in the night, they carried torches to guide them; when they labored at home, fire grew indispensable for baking their clay pottery, smelting their ore, and manifold purposes.