Phenomena are to the natural philosopher what organised beings are to the naturalist. He groups and classifies them on the same principles, and with a like object. And as the naturalist gives to each species a name applicable to the individual beings which exhibit corresponding qualities, so the philosopher gives to each force or attraction a name corresponding to the phenomena of which it is the cause. The naturalist is ignorant of the real essence or internal constitution of the thing which he nominates, and of the manner in which it comes to possess or exhibit those qualities which form the basis of his classification; and the natural philosopher is equally ignorant of the nature, seat, and mode of operation of the force which he assigns as the cause of an observed class of effects. These observations respecting the true import of the term “attraction” seem the more necessary to be premised, because the general phraseology of physical science, taken as language is commonly received, will seem to convey something more. The names of the several attractions which we shall have to notice, frequently refer the seat of the cause to specific objects, and seem to imply something respecting its mode of operation. Thus, when we say “the magnet attracts a piece of iron,” the true philosophical import of the words is, “that a piece of iron placed in the vicinity of the magnet, will move towards it, or placed in contact, will adhere to it, so that some force is necessary to separate them.” In the ordinary sense, however, something more than this simple fact is implied. It is insinuated that the magnet is the seat of the force which gives motion to the iron; that in the production of the phenomenon, the magnet is an _agent_ exerting a certain influence, of which the iron is the _subject_. Of all this, however, there is no proof; on the contrary, since the magnet must move towards the iron with just as much force as the iron moves towards the magnet, there is as much reason to place the seat of the force in the iron, and consider it as an agent affecting the magnet. But, in fact, the influence which produces this phenomenon may not be resident in either the one body or the other. It may be imagined to be a property of a medium in which both are placed, or to arise from some third body, the presence of which is not immediately observed. However attractive these and like speculations may be, they cannot be allowed a place in physical investigations, nor should consequences drawn from such hypotheses be allowed to taint our conclusions with their uncertainty. The student ought, therefore, to be aware, that whatever may seem to be implied by the language used in this science in relation to attractions, nothing is permitted to form the basis of reasoning respecting them except _their effects_; and whatever be the common signification of the terms used, it is to these effects, and to these alone, they should be referred.