To this corpuscular view, however, though it is unquestionably the sort of view to which, in our ultimate physical inquiries into the phenomena of matter, we must come, you may, perhaps, not be sufficiently accustomed, to enter fully into the reasoning on the subject. It will probably be less difficult for you, if we take rather, as an illustration, the simpler case of _impulse_; in which the bodies affecting each other are not, as in chemistry, indistinguishable corpuscles, but _masses_, clearly defined, and easily perceptible. I need not, of course, repeat the arguments formerly stated, to prove that _attraction_, however general it may be as a law of matter at all visible distances, does not continue, but gives place to an opposite tendency at those smaller distances, which we are unable to perceive with our weak organs, and which we learn to estimate only by effects that are inconsistent with absolute contact;--for example, by the well-known fact of the compressibility of bodies, which could not take place if their particles were already in contact, and which by continually increasing resistance to the compressing force that would bring the corpuscles nearer, shews, that there is, at different degrees of nearness, a tendency continuing to operate, which is the very reverse of attraction. There is, therefore, every reason to believe,--since repulsion, as the fact of forcible compression shews, takes place while the particles of bodies are still at a certain distance,--that the motion produced in one body by another, and ascribed to immediate impulse, is produced, without actual contact, by this mutual repulsion, as it is called, of the bodies when brought within a certain invisible degree of vicinity to each other; or, in other words,--for repulsion means nothing more mysterious than this simple fact,--the tendency which bodies, in certain relative positions of apparent but not actual contact, have to fly off from each other with certain degrees of velocity, as in certain other relative positions, of distinguishable distance, they have a tendency to approach each other. This repulsion, or tendency from each other at one point of nearness, is of itself as easy to be conceived, as that _attraction_, or tendency toward each other at other points of distance, to which we give the name of _gravitation_; and it is only from our greater familiarity with the one, as operating at distances which are visible, while the other,--except in a few cases, such as those of magnetism and electricity,--operates only at distances which are imperceptible to us, that we feel a little more difficulty in admitting the _repulsion_ than the _attraction_ of matter. There is then,--however universal gravitation may seem, when we think only of perceptible distances,--a certain point of near approach, before actual contact, at which gravitation ceases; and, beyond this point, the tendency of bodies toward each other is converted,--as the force