The vicar here interposed, observing that, simple as the question might appear to those who had studied it, the fact was so contrary to everything that passed before us, that Mr. Seymour ought not to feel any surprise at the scepticism of his daughter; he begged to remind him that the truth, apparent as it doubtless now was, lay hid for ages before the sagacity of Galileo brought it to light.
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.