§. 30. Connection of hearing with language.

One of the greatest benefits of the sense of hearing is, that, in consequence of it, we are enabled to hold intercourse with each other by means of language, without which the advancement of the human mind must have inevitably been very limited.

It is by language, that we express our feelings to the little company of our neighbours and our own family; and without it this pleasant and cheering intercourse must be almost entirely suspended. Not limited in its beneficial results to families and neighbourhoods, it is the medium of the transmission of thought from age to age, from generation to generation. So that in one age is concentrated the result of all the researches, the combination of the wisdom of all the preceding.

"There is without all doubt," it has been observed, "a chain of the thoughts of human kind, from the origin of the world down to the moment at which we exist,--a chain not less universal than that of the generation of every being, that lives. Ages have exerted their influence on ages; nations on nations; truths on errours; errours on truths."

Whether language be an invention of man, or a power bestowed upon him by his Creator and coeval with the human race, the ear must in either case have been the primary recipient; the faculty of speech so necessary and so beneficial could not have existed without the sense of hearing.

$. 31. Of the sense of touch.

The principal organ of touch is the hand. This part of our frame is composed of various articulations, that by the aid of the muscles are easily moveable, so that it can adapt itself readily to the various changes of form in the objects, to which it is applied.

The senses, which have been already mentioned, are more simple and uniform in their results, than that of the touch. By the ear we have a perception of sounds or that

sensation, which we denominate hearing. By the palate we have a knowledge of tastes, and by the sense of smelling we become acquainted with the odours of bodies. The knowledge, which is directly acquired by all these senses, is limited to the qualities, which have been mentioned. By the sense of touch, on the contrary, we become ac quainted not with one merely, but with a variety of qualities, such as the following, heat and cold, hardness and softness, roughness and smoothness, figure, solidity, motion, and extension.

Some might be inclined to say, that hardness and softness are expressive only of greater or less resistance, and are, therefore, the same thing, differing only in degree; but the consideration of these ideas separately does not properly come in here. In the remarks, which are hereafter to be made on the origin of knowledge, it will come within the plan of these Elements to bestow on some of them a more particular inquiry.

§. 32. Of the benefits of the sense of sight.

Of those instruments of perception, with which a benevolent Providence has furnished us, a high rank must be given to the sense of seeing. If we were restricted in the process of acquiring knowledge to the informations of the touch merely, how many embarrassments would attend our progress and how slow it would prove! Having never possessed sight, it would be many years, before the most acute and active person could form an idea of a mountain or even of a large edifice. But by the additional help of the sense of seeing, he not only observes the figure of large buildings, but is in a moment possessed of all the beauties of a wide and variegated landscape.

It does not fall within our plan to give a minute description of the eye, which belongs rather to the anatomist, but such a description, with a statement of the uses of the different parts of the organ, must be to a candid and reflecting mind a most powerful argument in proof of the existence and goodness of the Supreme Being. How won

derful among other things is the adaptation of the rays of light to the eye! If those minute particles, which come to us with such inconceivable rapidity from all things around us, were not coloured, we should be deprived of much of that high satisfaction, which we now take, in beholding surrounding objects; and if they were not of a texture so extremely small, they would cause much pain to the organ of vision.

§. 33. Statement of the mode or process in visual perception.

In the process of vision, the rays of light, coming from various objects and in various directions, strike in the first place on the pellucid part of the ball of the eye.

If they were to continue passing on precisely in the same direction, they would produce merely one mingled and indistinct expanse of colour.

In the progress through the chrystalline humour, they are refracted or bent from their former direction and distributed to certain focal points, on the retina, which is a white, fibrous expansion of the optick nerve.

The rays of light, coming from objects in the field of vision, whether it be more or less extensive, as soon as they have been distributed on their distinct portions of the retina, and have formed an image there, are immediately followed by the sensation or perception, which is termed sight.

The image, which is pictured on the retina, is the last step, which we are able to designate in the material part of the process in visual perception; the mental state follows, but it is not in our power to trace, even in the smallest degree, any physical connection between the optical image and the corresponding state of the mind.

All that we can say in this case is, that we suppose them to hold to each other the relation of antecedent and consequent by an ultimate law of our constitution.

NOTE. On certain terms used as synonymous.

The words, affection, idea, thought, sensation, operation, and perception are in common use indiscriminately applied to the mind, although some of them not exclusive. ly so; and when thus applied, appear to be used as synonymous, and as signifying merely a state or position of the thinking principle. It seems, therefore, to be useless to set up an arbitrary distinction between them, which the common speech, both in conversation and in writing, will be continually annulling; and which distinction, in the present almost indiscriminate application of the words, might tend rather to perplex than aid us in our inquiries. Be sides; nice inquiries into distinctions in the meaning of words belong rather to treatises purely philological than the present elementary work, which, taking language as it is, without pretending to define and settle its application, professes merely to collect for the use of the student, in a concise and plain view, some prominent facts in respect to the mind. Provided the facts are conveyed in an intelligible manner, so that the student can fully understand them, our object will be answered.

§. 34. Of the connection which the brain has with perception.

It was an odd opinion, which once widely prevailed, that our ideas are inscribed in marks or traces in the medullary substance of the brain. "So soon as the soul (says Malebranche in his Search after Truth) receives some new ideas, it imprints new traces in the brain, and so soon as the objects produce new traces, the soul receives new ideas."

This leads us to observe, without taking up time in remarking on this now exploded opinion, that the brain is a prominent organ in the material part of the process of sensation or of external perception. The sensorial substance, as it exists in the nerves, excepting the coat, in which it is enveloped, is the same as in the brain, being of the same

soft and partially fibrous texture and in perfect continuity with it. When the brain is in an unsound state, or has been in any way injured, both the external impression and the consequent perception are very imperfect. Also if the nerve, which is a supposed continuation of the brain, be injured, or if its continuity be disturbed by the pressure of a tight ligature, the effect is the same; both the external impression and the perception are either destroyed or are imperfect.

The brain, therefore, and the nerves in continuity with it constitute the sensorial organ, which in the subordinate organs of taste, of smell, of sight, of touch, and of hearing, presents itself under different modifications to external objects. On this organ, the sensorial, as thus explained, an impression must be made, before there can be perception.

An impression, for instance, is made on that part of the sensorial organ called the auditory nerve, and a state of mind immediately succeeds, which is termed the percep

tion of sound.

An impression is made by the rays of light on that expansion of the optick nerve, which forms what is termed the RETINA, and the intellectual principle is immediately brought into that new position, which is termed visual perception.

The hand is impressed on a body of an uneven and rough surface, and immediately consequent on this impression, is that state of mind, which is termed a sensation or perception of roughness.

§. 35. Impressions on the senses and perceptions are antecedents and consequents.

In all these cases, as we have already remarked in respect to sight in particular, the impression made on the organ of sense is the antecedent, the mental perception is the consequent, and we are utterly unable, further than the mere fact of precedence and sequence, to trace any connection between them. But while we can see in instances of this description no necessary, no physical connection