It is in accordance with modern scientific knowledge, to view the mind, not as a collection of distinct faculties, but rather as a single kind of power, like each of the physical forces, having several different modes of action; and as that which perceives, thinks, and wills. Its oneness is shewn by its inability to be simultaneously occupied by several diverse feelings, thoughts, or volitions, and by our incapacity to think of many varied ideas at once; the more ideas also or objects we attempt to perceive at once, the less we realize of each. In proportion as the mind is engaged upon one idea, so is it also unable to be occupied with another. Strong feelings exclude intellectual action. The mind can only execute several actions at a time, provided they have been rendered more or less automatic by habit, &c., but as all mental acts are in different degrees imperfectly automatic, and require more or less attention, and each individual mind is limited in its power, every such act withdraws a portion of attention from the more engrossing ideas. Power of mind and power of maintaining attention are nearly synonymous.
The recognised fundamental elements of mind are Receptivity and Perception of impression: Retentiveness of impression: Perception of agreement (or similarity) of impression: and Perception of difference
of impression. All purely mental acts appear to be resolvable into these.
Many persons still entertain the idea that mental actions are largely independent of the natural conditions to which physiological, chemical, and physical phenomena are subject. The unscientific mind is readily beguiled by easy schemes of mental action, or simple systems of mental and moral philosophy, unaware that great abstract truths often require deep thought to discover them, or even to perceive them when discovered and published. "A false notion, which is clear and precise, will always meet a greater number of adherents in the world than a true principle which is obscure." It is not until unscientific persons have become used to advanced scientific ideas and nomenclature, and knowledge as so far progressed as to enable thinking men to illustrate those ideas freely in familiar language, that great abstract truths are believed by the public. The ordinary and simple theory of the operations of the human mind is, that they often arise without any cause, and are frequently not obedient to ordinary influences, and this idea is still entertained and promulgated even by some of our most popular ministers of truth. It is therefore necessary in order to further prove that new scientific knowledge is really a basis of mental progress, to point out a few of the chief ways in which mental action essentially depends on scientific principles, and to adduce a few instances in which other substances than brain exhibit essentially similar phenomena. To
shew this however in a more satisfactory manner would require a large treatise to be written upon the subject.
The human brain and mind are evidently subject to the ordinary laws of matter and energy. Receptivity and retentiveness of impression is not only a property of brain, but of all solid matter without exception. Moser's pictures, and Chinese mirrors, the impressions on each being reproducible by warm breath, are examples of this. And as these two properties are fundamental elements of mind, they must be present in and essential to, every mental action.
All phenomena require time and all matter occupies space; thought and brain are no exception to this. Whilst all persons say "I must have time to think," many believe that thought is instantaneous. Time is a necessary condition of all thought, and therefore of all comparison, inference, imagination, and mental analysis; it takes time even to form an idea, or draw an inference from it, and the two cannot be formed simultaneously. Professor Donders, of Utrecht, has invented what he terms a Noëmatachograph for registering the amount of time occupied in mental processes, and by the aid of that instrument has ascertained that the time required by a man of middle age to perform a single act of simple thought is about one twenty-fifth part of a second. It has also been ascertained that the time required is longer in some persons than in others; and longer if the
subject of thought is one with which the thinker is not familiar. Mosso, by means of an instrument which he calls a Plethysmograph, has shewn, that during mental action, either in the waking state, or in dreaming, there is a greater amount of blood determined to the brain, and more during difficult than during easy mental action. These are instances of scientific research casting a light upon mental processes.
Coexistence of matter and energy is another great truth which appears to be applicable to all nature; wherever there is matter, there is either active or stored up power; and as particular forms of energy are in some cases most exhibited by particular kinds of substance, (as magnetism by iron), so mind is associated with living brain. As also we never see the physical powers exhibited except by material substance, so have we never yet observed mental action in a space devoid of material. The most perfect vacuum yet produced contains many millions of particles of substance in each cubic inch. Of all the countless number of scientific phenomena observed since men have been able to reliably investigate, not one has afforded us conclusive evidence of mental action entirely independent of these conditions. In accordance also with the usual truth in science, that complicated action requires complex structures; mind, being the most intricate action, is manifested by the most complicated body.
Mind, like each of the physical forces may be