In the first place, then, the interior sense differs from the exterior senses, in the property which it has of receiving all impressions, while the exterior senses receive them merely as they relate to their conformation; the eye, for example, being no more affected by sound than the ear is by light. Secondly, the interior differs from the exterior senses, by the duration of the agitations produced by exterior causes; but in every other respect they are of the same nature. The interior sense of the brute, as its exterior, is entirely material, and the effect of mechanical organization. We have, like the animal, this material sense; and we possess, moreover, a sense of a nature highly superior, which resides in the spiritual substance, and which animates and guides us. The brain of the animal is, therefore, a general sense, which receives all impressions the external senses transmit to it, and these impressions continue much longer in the internal than in the external senses: for instance, the agitations which light produces in the eye, continues longer than that which sound produces on the ear. It is on this account that the impressions, which the former transmits to the interior sense, are more strong than those transmitted by the latter; and that we represent to ourselves the things which we have seen much more forcibly than those which we have heard. It is even found, that of all the senses, the eye is that in which the agitations are the most durable, and in which, of consequence, though seemingly they are more explicit, the strongest impressions are formed. The eye may therefore be considered as a continuation of the interior sense. It is, indeed, nothing more than one large nerve expanded, and a prolongation of the organ, in which the interior sense resides. That in its nature there should be a greater affinity to this internal sense is not then surprising; and in effect not only its impressions are more durable, but its properties more eminent than those of the other senses. The eye represents outwardly the inward impressions. Like the internal sense, it is active, and expresses desire or aversion, while all the other senses are wholly passive; they are merely organs formed for the reception of exterior impressions, but incapable of retaining or reflecting them. When with violence, however, and for a length of time any sense is acted upon, the agitation subsists much longer than the action of the exterior objects. This is, however, felt most powerfully in the eye, which will retain the dazzling impression made by looking for a moment on the sun, for hours and even days.