On flame. / Where flame is generated, there is generated wind surrounding it, whose course serves to feed and increase that flame. / Second. — The motion of that wind will be the more impetuous, the greater the quantity of flame it has to feed. / Third. — That flame will be of greater heat which is the more splendid; and the converse follows: that one will be the more splendid which is of greater heat. / And that flame will be of greater splendour which is generated in air of swifter motion; and that will be of swifter motion which is the more splendid. / That flame will extend to greater length which is generated in air of more excellent heat; and, conversely, it will be of shorter length which is generated in a place of greater cold.

b c a / The motion of the flame, together with the wind that is generated by it, will be circular if it is fed by material of uniform nourishment, and such circulation will be parallel; that is, such a circle will be of empty circulation, that is, annular. Thus the growth of the fire moves against the wind that of itself nourishes it; but the opposite wind generated around the centre of such circulation jousts against the wind generated outside that circle, and within their encounters they enclose and strike the flame, and their percussion is reflected and leaps back toward the sky, carrying with it the flame that has been generated. / The wind generated within the annular fire descends from above and not from below, and that generated outside this ring moves from below to above, as will be proved. / The element of fire continually consumes the air that in part nourishes it, and it would remain in contact with a vacuum if the succeeding air did not come to fill it. But the place from which such succour departed would itself remain empty, and so it would follow successively if the succeeding air did not continually fill with itself the place left by the preceding motion of the air; and so it would continue as far as the sphere of water. But the air that borders on the water is, with its exhalation or vaporisation, of such thickness that it would continually make sufficient replenishment of every kind of vacuum whatsoever that might be generated above it, etcetera.

That nourishment will make less smoke which has in itself a smaller quantity of moisture. / That smoke is darker which has in itself more moisture. The excessive final smoke arises from the excessive moisture infused in the material that fed the flame. / In materials of equal moisture, that one will make less smoke in proportion as it is of a greater quantity of nourishing material, that is, of wood. / And this arises because where there is more wood, there is more flame, and where there is more flame, more nourishment is consumed, and so conversely. But such consumption is not in proportion to the flame generated from it, etcetera. / The flame has its beginning and end from smoke. / The smoke from which the flame is generated is of much greater heat than the smoke in which that flame ends, because in the first smoke is the nourishing virtue of the flame, and the last is the mortal failing of the same flame. / Young and dry wood generates more blue smoke than old and damp wood.

Along the right margin.

Of the sum of the joined flames, that one will be the more elevated which lies over greater nourishment. It follows that that one will be the smaller which is fed by lesser nourishment.