Mr. Seymour admitted the justice of this remark, and proceeded in his explanation. “I think,” said he “you will readily allow that matter cannot, in itself, possess any power of changing its condition: it can, therefore, no more destroy, than it can originate its own motion; when it is at rest, it must ever remain so, unless some force be applied that can impart to it activity; and, when once in motion, it must continue to move until some counteracting force stops it. To believe otherwise you must suppose that matter possesses in itself a power to alter its condition, which is perfectly absurd.” “And yet,” said Tom, “when I see my ball or marble stop of its own accord, how can you blame me for believing it possible?” “Your difficulty arises from your ignorance of the existence of certain forces which act upon the rolling ball or marble. Its progress, as it rolls along, is impeded and ultimately stopped by the rubbing, or friction, occasioned by its passage over the ground; and this will be greater or less, according to the degree of roughness of the surface; if it be small, the ball will continue for a longer time in motion; you must have observed, that your marble has always rolled much farther on a smooth pavement than on a rough gravel walk.” “Certainly,” said Tom, “and I well remember, that when we played at _ring-taw_ last winter on the ice, we were obliged, for this very reason, to extend the usual boundaries.” “Is it not evident, then, that the motion of a body is stopped by some opposing force; and that, if this could be entirely removed, the body would continue to move for ever?” “What a provoking thing this friction is,” said Tom, “it is always interfering with our experiments.” “Provoking, is it? I fancy,” said Mr. Seymour, “that you would be much more provoked by the loss of it: without it, you could not walk, nor even hold an object in your hands; and yet everything around you would be in perpetual motion, performing one universal and interminable dance.” “I can readily understand, from what you have said, that, if friction were removed, motion might continue; but pray how is it that we should be unable to walk, or to hold anything in our hands?” enquired Louisa. “It is the friction of the ground which, at every step we take, prevents the foot from sliding back, and thus enables us to push the body forwards. Everybody must have felt how difficult it is to walk on ice, where the friction is only diminished, not entirely removed,” answered her father; “and as to holding any object,” continued he, “it is the friction of the body to which we apply our hands that enables us to hold it firmly.” “To be sure,” exclaimed the vicar; “why, my boy, you must surely remember, that in ancient combats it was the custom to rub the body with oil, that the adversary might not be able to keep his grasp.” “Well,” said Tom, “our houses, I suppose, would remain firm, and we might sit quietly in our chairs, at all events.”