Gravity, or the tendency of a body to approach the earth, is proportioned to the _square of the distance_; that is, if a body be attracted by the earth at a certain distance, with a certain force, and be afterwards removed to _twice_ the distance, it will now be attracted, not _half_ us much, but only _one-fourth_ as much as it was before; and if it be removed to _three_ times the first distance, it will be attracted not _one-third_ as much, but _one-ninth_, as much as before; four being the square of two, and nine the square of three. Footnote 8: In the legends of Scottish superstition, the magic power of imposing upon the eye-sight was termed _Glamour_. “It had much of glamour might: Could make a ladye seem a knight; The cobwebs on a dungeon wall, Seem tapestry in lordly hall; A nutshell seem a gilded barge, A sheeling seem a palace large, And youth seem age, and age seem youth:-- All was delusion, nought was truth.”         _Lay of the Last Minstrel._--Canto 3. ix. CHAPTER III. _Motion--absolute and relative.--Uniform, accelerated, and retarded Velocity.--The times of Ascent and Descent are equal.--Vis inertiæ.--Friction.--Action and Reaction are equal and in opposite directions.--Momentum defined and explained.--The Three Great Laws of Motion._ “The table-cloth is removed,” cried Tom, as he cast a sly glance through the open window of the dining-room. “It is, my boy,” replied Mr. Twaddleton; “_Diffugere nives_, as the poet has it.” “_Et redeunt jam gramina campis_,” added Mr. Seymour, archly, as he pointed to the green cloth with which the table was covered. “_Et decrescentia flumina_,” continued the vicar, with a smile; “but, psha! enough of wine and quotation. Come, let us join the children.” Mr. Twaddleton, accompanied by Mr. and Mrs. Seymour, and Louisa, rose from the table, and proceeded to the lawn. “The gravitation of Tom’s ball,” said Mr. Seymour, “furnished an ample subject for our morning’s diversion; let us try whether its other motions will not suggest further objects of enquiry.” “I well remember,” observed Louisa, “that Mrs. Marcet extols that apple, the fall of which attracted the notice of Sir Isaac Newton, above all the apples that have ever been sung by the poets: and she declares, that the apple presented to Venus by Paris; the golden apples by which Atalanta won the race; nay, even the apple which William Tell shot from the head of his own son, cannot be brought into comparison with it.” “Well said! Mrs. Marcet,” exclaimed Mr. Seymour; “upon my word, had the mother of mankind used but half such eloquence in praise of an apple, we cannot wonder at its influence.” “What honours, then,” continued Louisa, “shall we decree to Tom’s ball, if it instructs us in the first principles of philosophy?”