_The kind of Knowledge afforded by the Senses._--It is to be noticed, in addition, that with the exception of the tactual sense, and possibly of sight, these senses give us no direct, immediate knowledge of external things. They simply furnish data, signs, intimations, by the help of which the understanding forms its conclusions of the world with out. They are the _receiving_ agents of the mind. This is, in fact, the chief office of sense, to receive through its various avenues the materials from which the understanding shall frame conceptions of things without; to convey, as it were, a series of telegraphic despatches along those curious and slender filaments that compose the nervous organization, by means of which the soul, keeping her hidden seat and chamber within, may receive communication from the distant provinces of her empire. These signs the understanding interprets; and in so far as this is the true nature of the process, it is not a process of immediate and proper perception. I hear, for example, a noise. All that I really perceive in this case is the sensation of sound. I refer it, however, to an external cause, to a carriage passing in the street. I specify, moreover, the kind of carriage, perhaps a coach, or a wagon with iron axles. I have observed, have learned by experience, that sounds of this nature are produced in this way, that is, by carriages passing, and by such carriages. Hence I judge that the sound which I now hear is produced in the same way. It is an _inference_, a conception merely. All that sense does is to receive and transmit the sign, which the understanding interprets by the aid of former experience. And the same is true of the other senses, with the exceptions named. _Not therefore of little Value._--We are not to infer, however, that these senses are on this account of no special value or importance to us. They do precisely what is needed. They put us in possession of just the data wanted in order to the necessary information concerning external things. It is only the theorist who undervalues the senses, and he only in his closet. No man, in the full possession of his reason, and his right mind, can go forth into this fair and goodly world, and not thank God for every one of those senses--sight, hearing, taste, touch, and smell. Their true and full value, however, we never learn till we come to be deprived of their use; till with Milton we exclaim, "Seasons return; but not to me returns Day, or the sweet approach of even or morn." § V.--AMOUNT OF INFORMATION DERIVED FROM THE RESPECTIVE SENSES _A further Question as to one Class of the Senses._--The relations and specific functions of the several senses have been already described. Some further questions arise, however, respecting the precise amount and kind of information afforded by that class of the senses which; as we have seen, relates to the spatial properties of bodies, in distinction from the chemical, viz.: hearing, sight, and touch.