Fire. On the boiling of water. The water that is in contact with the bottom of the heated vessel is at once converted into air mixed with fire. This is proved by the foregoing, which said that the part of the air which shares most in heat rises highest. Hence the exhalation of the water penetrates above the low region of the air that is in contact with it, being mixed with the element of fire, which carries it along with itself as it returns home to its sphere.

Rings for the arms of such a mixture, and the gold clasp with jewels. Why the bubbles leap out of the vessel where the water boils. The bubbles of the water are driven out of their vessel with force by the weight of the water that rests upon them. And this force is as much swifter than the mere air that rises from the bottom of marshes as it is in greater quantity and of greater heat.

Which resists more under one and the same depth of water, the little air or the much?

The water rises from the bottom of the river in three ways: that is, either it rises with a slow welling, or it is driven up by a bellows, or it is driven up by fire that heats it from below and it vaporizes with a continuous welling.

When c is at a, a is at c, and thus the wheel and the moving body have made half a turn.

The levelness of the surface of a motionless liquid will not be altered from the levelness of the surface of the liquid heavier than it which surrounds it with its contact.

On the smoke of the extinguished candle. The smoke of the extinguished candle has its edges denser than its middle, because it turns back toward the middle, fleeing from the resistance of the cold air where it strikes in its expansion; and because it can rarefy and condense, it grows dense at its extremities. In this case it does not behave like water, which, since it cannot of itself either rarefy or condense, is of necessity such that the part reflected from the place of the impact forms a wave which moves over the oncoming water in a contrary motion.

The point is said to have no part, and from this it follows that it is indivisible; and indivisible things have no middle, and whatever has no middle is bounded by nothing. Hence the point is nothing, and upon nothing no science can be begun. And to escape such a beginning we shall say: the point is that than which nothing can be smaller; and the line is created by the motion of the point, than which nothing can be narrower or thinner, and its ends are two points; and the surface is generated by the crosswise motion of the line, than which nothing can be thinner, and its ends are lines; and the body is made by motion. Another way. The point has no middle, and its ends are nothing. The line is a length made by the motion of the point, and its ends are two points, and the ends of its breadth and depth are nothing. The surface is created by the crosswise motion of the line, and its ends are lines, and its depth is nothing. The body is generated by motion. The converse: The point is generated where the length of the line ends; the line is born where the breadth or length of the surface ends; and the surface is created at the limit of the breadth, length and depth of the body. The point is the common boundary between nothing and the front of the line; it is neither part of the line, nor part of nothing, nor does it occupy a place between nothing and the line. Hence the end of nothing and the beginning of the line are in contact with one another, without any other interval following. If the surface is not part of a body, nor part of the air with which it is bounded, nor part of the body which it surrounds, and nothing else is interposed between the air and the body, what can we say such a surface to be other than nothing? If the surface is neither part of the body clothed by it nor part of the air by which it is surrounded? Nothing is born at the boundary of the thing. Where nothing ends, the thing is born; and where the thing fails, nothing is born.