The elements in mediaeval cosmology were assigned to a definite region of the universe. Being mortal and imperfect they occupied four spheres below the moon, the elemental region or region of imperfection, as distinguished from the ethereal region above the moon. Immediately within the sphere of the moon came that of Fire, below this the Air, then Water, and lowest of all the solid sphere of Earth. Fire being the most ethereal of the elements constantly tends to rise upward, while Earth sinks towards the center of the universe. This contrast is a favorite idea with Dante, who says in the _Paradiso_ i. 112-117: "'wherefore they move to diverse ports o'er the great sea of being, and each one with instinct given it to bear it on. This beareth the fire toward the moon; this is the mover in the hearts of things that die; this doth draw the earth together and unite it.'" Elsewhere Dante describes the lightning as fleeing its proper place when it strikes the earth: "'but lightning, fleeing its proper site, ne'er darted as dost thou who art returning thither.'"[39] And again: "'so from this course sometimes departeth the creature that hath power, thus thrust, to swerve to-ward some other part, (even as fire may be seen to dart down from the cloud) if its first rush be wrenched aside to earth by false seeming pleasure.'"[40] The same thought of the tendency of fire to rise and of earth to sink is found in Chaucer's translation of Boethius:[41] "Thou bindest the elements by noumbres proporcionables, ... that the fyr, that is purest, ne flee nat over hye, ne that the hevinesse ne drawe nat adoun over-lowe the erthes that ben plounged in the wateres." Chaucer does not make specific mention of the spheres of the elements, but he tells us plainly that each element has been assigned its proper region from which it may not escape: "For with that faire cheyne of love he bond The fyr, the eyr, the water, and the lond In certeyn boundes, that they may nat flee;"[42] The position of the elements in the universe is nevertheless made clear without specific reference to their respective spheres. The spirit of the slain Troilus ascends through the spheres to the seventh heaven, leaving behind the elements: "And whan that he was slayn in this manere, His lighte goost ful blisfully is went Up to the holownesse of the seventh spere, In converse letinge every element."[43]