After having considered the waters, let us now contemplate another mass yet of far greater extent.  Do you see what is called air?  It is a body so pure, so subtle, and so transparent, that the rays of the stars, seated at a distance almost infinite from us, pierce quite through it, without difficulty, and in an instant, to light our eyes.  Had this fluid body been a little less subtle, it would either have intercepted the day from us, or at most would have left us but a duskish and confused light, just as when the air is filled with thick fogs.  We live plunged in abysses of air, as fishes do in abysses of water.  As the water, if it were subtilised, would become a kind of air, which would occasion the death of fishes, so the air would deprive us of breath if it should become more humid and thicker.  In such a case we should drown in the waves of that thickened air, just as a terrestrial animal drowns in the sea.  Who is it that has so nicely purified that air we breathe?  If it were thicker it would stifle us; and if it were too subtle it would want that softness which continually feeds the vitals of man.  We should be sensible everywhere of what we experience on the top of the highest mountains, where the air is so thin that it yields no sufficient moisture and nourishment for the lungs.  But what invisible power raises and lays so suddenly the storms of that great fluid body, of which those of the sea are only consequences?  From what treasury come forth the winds that purify the air, cool scorching heats, temper the sharpness of winter, and in an instant change the whole face of heaven?  On the wings of those winds the clouds fly from one end of the horizon to the other.  It is known that certain winds blow in certain seas, at some stated seasons.  They continue a fixed time, and others succeed them, as it were on purpose, to render navigation both commodious and regular:  so that if men are but as patient, and as punctual as the winds, they may, with ease, perform the longest voyages.

Sect.  XV.  Of Fire.

Do you see that fire that seems kindled in the stars, and spreads its light on all sides?  Do you see that flame which certain mountains vomit up, and which the earth feeds with sulphur within its entrails?  That same fire peaceably lurks in the veins of flints, and expects to break out, till the collision of another body excites it to shock cities and mountains.  Man has found the way to kindle it, and apply it to all his uses, both to bend the hardest metals, and to feed with wood, even in the most frozen climes, a flame that serves him instead of the sun, when the sun removes from him.  That subtle flame glides and penetrates into all seeds.  It is, as it were, the soul of all living things; it consumes all that is impure, and renews what it has purified.  Fire lends its force and activity to weak men.  It blows up, on a sudden, buildings and rocks.  But have we a mind to confine it to a more moderate use?  It warms man, and makes all sorts of food fit for his eating.  The ancients, in admiration of fire, believed it to be a celestial gift, which man had stolen from the gods.