“Not so,” replied Mr. Seymour, “for even granting that you had houses and chairs, which, without the existence of friction would never exist, the stability of the structures could never be secured; the slightest breath would be sufficient to make the stones or bricks slide off from each other, and to reduce your dwellings into dancing ruins.” Tom and Louisa, after some farther discussion, both admitted the justness of the argument; but, at the same time, would have been better satisfied if the fact could have been proved by actual experiment. Mr. Seymour told them that the perpetual revolution of the earth and heavenly bodies, where no friction whatever existed, afforded a proof which ought to satisfy them; and, especially, since it agreed with those views which were proved to be true by an examination of what took place on the surface of our own globe. We will, therefore, with the permission of our readers, consider this point as settled, and proceed with the young philosophers to the investigation of some other topics connected with the doctrine of motion. “Since a body at rest,” said Mr. Seymour, “can only be set in motion, or, when in motion, be brought to rest, by the impression of some force, it must follow, that it can only move in the direction in which such a force may act; and, moreover, that the degree of motion, or the _velocity_, must, other things being equal, be in proportion to the degree of force used.” “Why, truly,” cried the vicar, “my young friends must of necessity admit that fact; for the body, not having any will of its own, as you say, must needs, if it move at all, go the road it is driven.” “Yes,” added Mr. Seymour, “and it must go with a velocity in proportion to the force with which it is driven.” “Doubtless, doubtless,” cried the vicar, “you admit that also; do you not, my young friends and playmates?” It is hardly necessary to state, that the children instantly assented to these propositions. The vicar had placed them in so clear and popular a point of view, as to be intelligible to the lowest capacities. “With these admissions, then, my dear children,” said their father, “I shall have but little difficulty in convincing you of the truth of the other laws by which the direction of moving bodies is governed. At present, however, it is not my intention to enter upon this subject; you have some preliminary knowledge to acquire before you can understand what is termed the _Composition and Resolution of Forces_.” “I shall not easily forget,” said Louisa, “that matter is perfectly passive, and that it can neither put itself in motion when at rest, nor stop itself when in motion.” “This indifference to rest or motion,” replied Mr. Seymour, “has been termed the _Vis Inertiæ_ of matter.”