The senses in general, and especially the sight, are a vapour of excessive warmth, and on this account a man is said to see through air, and through water. For the hot principle is opposed by the cold one; since, if the vapour in the eyes were cold, it would have the same temperature as the air, and so would be dissipated. As it is, in some passages he calls the eyes the gates of the sun. And he speaks in a similar manner of hearing, and of the other senses. He also says that the soul of man is divided into three parts; into intuition (νοῦς), and reason (φρὴν), and mind (θυμὸς), and that the first and last divisions are found also in other animals, but that the middle one, reason, is only found in man. And that the chief abode of the soul is in those parts of the body which are between the heart and the brain. And that that portion of it which is in the heart is the mind (θυμὸς); but that deliberation (νοὺς), and reason (φρὴν), reside in the brain.[113] Moreover, that the senses are drops from them; and that the reasoning sense is immortal, but the others are mortal. And that the soul is nourished by the blood; and that reasons are the winds of the soul. That it is invisible, and so are its reasons, since the æther itself is invisible. That the links of the soul are the veins, and the arteries, and the nerves. But that when it is vigorous, and is by itself in a quiescent state, then its links are words and actions. That when it is cast forth upon the earth it wanders about, resembling the body. Moreover, that Mercury is the steward of the souls, and that on this account he has the name of Conductor, and Commercial, and Infernal, since it is he who conducts the souls from their bodies, and from earth, and sea; and that he conducts the pure souls to the highest region, and that he does not allow the impure ones to approach them, nor to come near one another; but commits them to be bound in indissoluble fetters by the Furies. The Pythagoreans also assert, that the whole air is full of souls, and that these are those which are accounted dæmones, and heroes. Also, that it is by them that dreams are sent among men, and also the tokens of disease and health; these last too, being sent not only to men, but to sheep also, and other cattle. Also, that it is they who are concerned with purifications, and expiations, and all kinds of divination, and oracular predictions, and things of that kind. They also say, that the most important privilege in man is, the being able to persuade his soul to either good or bad. And that men are happy when they have a good soul; yet, that they are never quiet, and that they never retain the same mind long. Also, that an oath is justice; and that on that account, Jupiter is called Jupiter of Oaths (Ὅρκιος). Also, that virtue is harmony, and health, and universal good, and God; on which account everything owes its existence and consistency to harmony. Also, that friendship is a harmonious equality.