Panvotrus saith:—I signify to posterity that air is a tenuous matter of water, and that it is not separated from it. It remains above the dry earth, to wit, the air hidden in the water, which is under the earth. If this air did not exist, the earth would not remain above the humid water. They answer:—Thou hast said well; complete, therefore, thy speech. Sut he continueth: The air which is hidden in the water under the earth is that which sustains the earth, lest it should be plunged into the said water; and it, moreover, prevents the earth from being overflowed by that water. The province of the air is, therefore, to fill up and to make separation between diverse things, that is to say, water and earth, and it is constituted a peacemaker between hostile things, namely, water and fire, dividing these, lest they destroy one another. The Turba saith:—If you gave an illustration hereof, it would be clearer to those who do not understand. He answereth:—An egg is an illustration, for therein four things are conjoined; the visible cortex or shell represents the earth, and the albumen, or white part, is the water.* But a very thin inner cortex is joined to the outer cortex, representing, as I have signified to you, the separating medium between earth and water, namely, that air which divides the earth from the water. The yolk also of the egg represents fire; the cortex which contains the yolk corresponds to that other air which separates the water from the fire. But they are both one and the same air, namely, that which separates things frigid, the earth from the water, and that which separates the water from the fire. But the lower air is thicker than the upper air, and the upper air is more rare and subtle, being nearer to the fire than the lower air. In the egg, therefore, are four things—earth, water, air, and fire. But the point of the Sun, these four excepted, is in the centre of the yolk, and this is the chicken. Consequently, all philosophers in this most excellent art have described the egg as an example, which same thing they have set over their work.