9. Once more ; it is obvious that with out any external excitement of the nerves by which muscular motion is produced, the, mind can produce such motion ; in other words, that state of the motory nerves by which muscular motion is ef fected, can be produced by the mind. We do not here inquire how the mind learns to use its influence over the motory nerves, but state the fact, that muscular motion can be produced by the mind without ex ternal excitement. To account for this, we infer that the mind possesses a power or capacity of influencing the motory nerves so as to produce muscular motion, which may be called the motive power.— We have no name appropriate to those states of mind which produce the changes in the motory nerves requisite for muscu lar motion ; and we are, therefbre, so far free from a difficulty which has accom panied us when speaking of sensations and ideas i these terms, as they are gene rally used, imply that the consciousness of the mind is excited. But it appears an almost indisputable fact, that the mental organs, whatever they be, by whose ac tion the consciousness is excited, often are in a state of activity without such ex citement of the consciousness ; in other words, that those changes which, when accompanied with consciousness, are termed sensations and ideas, may take place, and produce their appropriate ef fect in the mental system, without excit ing the conscious or percipient principle. In order to enter into the consideration of this important fact, it will be necessary to consider somewhat more explicitly, in what manner we employ the term mind, and to introduce some less customary terms, in order to avoid ambiguity.
10. In the philosophical sense of the term mind, it seems to belong exclusive. ly to the conscious or percipient princi ple, whatever that be; but in common language we certainly employ it differ ently: e. g. no one hesitates in saying, "such a man has an extensive store of knowledge in his mind;" but no one supposes that at any one time a man per ceives, that is, is conscious of, all the parts of that knowledge: in the same manner no one would hesitate in saying, "such a person has a great fund of valua ble reflections for the conduct of life stored up in his mind, which he can pro duce whenever circumstances call for them;" but no one supposes that those reflections are always in the view of his mind, that is, that he is always conscious of them, that he always perceives them, All that can be meant in such cases, is, that the causes of his ideas (that is of his thoughts and feelings) remain in the mind, ready for excitement when they produce ideas.—Hence then the mind, in the common acceptation of the term in which we use it, consists of two parts, the conscious or percipient princi ple, and the organized substance, which furnishes to the former the objects of its consciousness or percipiency. What the conscious or percipient principle is, is probably known to him only who formed it: we may believe consciousness or per cipiency to be a property which is the necessary result of, or added to, a cer tain organized system of matter; or we may believe it to be a property of some substance essentially different from mat ter ; and we apprehend it is not of much consequence which opinion is adopted: but it seems indisputable, that in the present state of knowledge, we cannot obtain, on either side, more than a bare preponderance of probabilities.
11. That organized substance, which, without any further medium, furnishes to the conscious or percipient principle the objects of consciousness or percipiency, may he called the sensorium. The parts of which the sensorium is composed, by whose motions or other changes, without any further medium, consciousness is excited, may be called the mental organs. By the mind, we understand the whole together, the conscious or percipient principle together with the sensorium ; leaving it undecided, whether conscious ness is a property of organized matter, or belongs to a substance essentially dif ferent from matter; and also, whether the sensorium be or be not the medullary sub stance of the brain. (See SENSATION.) Hartley, as is well known, adopts the affirmative in the latter case; and he supposes that the changes of the sensori um which affect the consciousness are vibrations, of the medullary substance (see VIBILATION) ; we consider this hy pothesis as a clog upon, at least, the adoption of his grand system of associa tion, and should prefer the more gene ral term, motions, if we professed to de cide respecting the nature of the senso rium ; as we do not, we shall employ the still more general term changes, since the term affections is already appropri ated.—The changes in the sensorium, or mental organs, which may excite the con sciousness, may be called sensorial chan ges. Of these some are produced by the impression of external objects upon the organs of sense ; these may be called sensible changes ; others, as we know by their effects, are producible without the presence of external objects; these may be called ideal changes, and are the re licts of sensible changes ; a third class are those which are followed by muscu action, and may be termed motory changes. Each of these classes of sen sorial changes may take place without consciousness, as we shall endeavour to show in the next paragraph. When sensible changes are accompanied with consciousness, they are called sensations; when ideal changes are accompanied with consciousness, they are called and as sensible and ideal changes are princi pally important to us when accompanied with consciousness, and it seldom is ne cessary to distinguish between those which do and those which do not excite it, we shall not usually depart from the customary nomenclature. We have no term appropriated to denote motory changes accompanied with conscious ness: this deficiency probably arises from the circumstance, that muscular action is so much an object of the senses, that by association it is referred to the moving muscle, and not to the intermediate fibrous motions and sensorial changes; thus, while writing, all the motion seems to be in the fingers, and in the fingers alone, though even the minutest motion, except that which is produced by some external stimulus upon the motory nerve, implies motory changes of the sensorium, and should, scientifically speaking, be referred to the sensorium, or mind.