“I well remember the trick to which you allude. The rotatory motion prevented the sword from falling, just as you will hereafter find the spinning of the top will preserve it in an erect position. There is also another effect produced by rotatory motion, with which it is essential that you should become acquainted. You, no doubt, remember that momentum, or the velocity of a body, will compensate for its want of matter. A number of bodies, therefore, although incapable of balancing each other when in a state of rest, may be made to do so, by imparting to them different degrees of motion. I believe that you are now acquainted with all the principles upon which the art of balancing depends; and I have little doubt, should we again witness a performance of this kind, that you will be able to explain the tricks which formerly appeared to you so miraculous.” [Illustration: Three boys using stilts.] ----- Footnote 9: In Scotland stilts are used to pass rivers. Footnote 10: A The vicar here alludes to the speech of Moloch (Paradise Lost, b. ii. 1. 75):-- “That in our proper motion we ascend Up to our native seat: descent and fall To us is adverse.” ------------------------------------------------------------------------ [Illustration: A man holding a balloon with a face on it, blown up, and six people laughing at the sight.] CHAPTER V. _The Chinese Tumblers, illustrating the joint effects of change in the centre of gravity of a body, and of momentum.--Mr. Twaddleton’s arrival after a series of adventures.--The Dancing Balls.--The Pea-shooter.--A figure that dances on a fountain.--The Flying Witch.--Elasticity.--Springs.--The game of “Ricochet,” or Duck and Drake.--The Rebounding Ball.--Animals that leap by means of an elastic apparatus.--A new species of puffing, by which the Vicar is made to change countenance._ Early on Monday morning did the young group assemble in the library; they had been told by Mrs. Seymour that their father had received a new toy of a very interesting and instructive nature, and we can easily imagine the eagerness with which they anticipated the sight of it. “I trust,” said Mr. Seymour, “that after our late discussion, the subject of the centre of gravity is thoroughly understood by you all. I have also reason to think that the nature and effects of what is termed _momentum_ have been rendered intelligible to you.” “I certainly understand both those subjects,” answered Tom; and so thought the rest of the party.