Of Aristotle’s conception of a fifth element, the quinta essentia, or ether, superior to the others and permeating them, Isidore shows merely a trace. He says in one passage that “ether is the place where the stars are, and it signifies that fire which is separated on high from all the universe”.[73] He offers also another definition in which he confuses three of the elements of Aristotle: “Ether is the upper, fiery air”.[74]
The theory of the four elements, as has been already indicated, has a cosmological bearing. In the universe at large the elements were thought of as tending to arrange themselves in strata according to weight. Isidore says it is proved “that earth is the heaviest of all things created; and therefore, they say, it holds the lowest place in the creation, because by nature nothing but itself can support it. And we perceive that water is heavier than air in proportion as it is lighter than earth.... Fire, too, is apprehended to be in its nature above air, which is easily proved even in the case of fire that burns in earthy substance, since as soon as it is kindled, it directs its flame toward the upper spaces which are above the air, where there is an abundance of it, and where it has its place.”[75]
Thus the physical universe consists of the four kinds of matter, stratified according to the principle of weight. The notion was one in frequent use,[76] and it was brought into relation with animate existence by assigning to each of the four strata a peculiar population. Thus the fiery heavens were occupied by angels; the air, by birds and demons; the water, by fishes; the earth, by man and other animals.[77]
The theory of the four elements was fertile in every branch of the natural science of medieval times. Isidore uses it, for example, to explain the physical constitution of man:
Man’s body is divided among the four elements. For he has in him something of fire, of air, of water, and of earth. There is the quality of earth in the flesh, of moisture in the blood, of air in the breath, of fire in the vital heat. Moreover, the four-fold division of the human body indicates the four elements. For the head is related to the heavens, and in it are two eyes, as it were the luminaries of the sun and moon. The breast is akin to the air, because the breathings are emitted from it as the breath of the winds from the air. The belly is likened to the sea, because of the collection of all the humors, the gathering of the waters as it were. The feet, finally, are compared to the earth, because they are dry like the earth. Further, the mind is placed in the citadel of the head like God in the heavens, to look upon and govern all from a high place.[78]
In another passage Isidore tells us that fire has its seat in the liver, and that “it flies thence up to the head as if to the heavens of our body. From this fire the rays of the eyes flash, and from the middle of it, as from a center, narrow passages lead not only to the eyes but to the other senses”.[79]
Naturally the four elements play a great part in medicine. They are related to the four humors, blood, yellow bile, black bile, and phlegm. “Each humor imitates its element; blood, air;[80] yellow bile, fire; black bile, earth; phlegm, water. Health depends on the proper blending of these humors.”[81] It appears to have been the belief of the time that the humors possessed each the same qualities as the corresponding element. Medical reasoning might confine itself to the four humors or it might go back of them to the four elements, as in the explanation of vertigo, where the diagnosis indicates, apparently, the transmutation of one element into another. Isidore says: “The arteriae [air passages] and veins produce a windiness in man’s head from a resolving of moisture, and make a whirling in his eyes whence it is called vertigo”.[82]
That notions of such a loose, semi-philosophical nature should survive while the solid empirical content of medical science faded away, is characteristic of the decline of thought which culminated in the dark ages. The science of medicine had cut itself loose from concrete things, and attached itself almost exclusively to the vague philosophical conceptions from which even the best Greek thinkers had not been able to free it.
The phenomena of meteorology, also, were explained largely by the four elements. The upper air was believed to be akin to the fire above it, and was therefore calm and cloudless; while the lower air was supposed to be cloudy and disturbed by storms because of its proximity to water, the next element below it in the series.[83] Further, the belief in the possibility of the transmutation of elements was of use here. Air, for example, might be transmuted into water, or water into air.[84] As Isidore puts it: “[air] being contracted, makes clouds; being thickened, rain; when the clouds freeze, snow; when thick clouds freeze in a more disordered way, hail; being spread abroad, it causes fine weather, for it is well-known that thick air is a cloud, and a rarified and spread-out cloud is air.”[85]
Fig. 2.