“The first tyme that he, the prince, went to the towne of Sterling to meete the king, seeing a little without the gate of the towne a stack of corne, in proportion not unlike to a topp, wherewith he used to play, he said to some that were with him, ‘Loe there is a goodly topp:’ whereupon one of them saying, ‘Why doe you not play with it then?’ he answered, ‘Set you it up for me, and I will play with it.’” “Was not that a clever retort of the young prince?” said the vicar, as he returned the manuscript into his memorandum-book; “and I think it must have confounded the courtier who could have asked so silly a question.” “Well, Tom,” said Mr. Seymour, “let us see whether you can set up your own top, so that it shall stand steadily on its point.” “I have often tried that experiment,” answered Tom, “but could never succeed in keeping the line of direction within its narrow base.” “And yet, when in rotatory motion, its erect position is maintained without difficulty; how is that?” “Is it not owing to the centrifugal force?” asked Tom. “Undoubtedly: but as the subject is highly interesting, I will endeavour to explain it more fully. You must, however, first obtain permission from the vicar to spin your humming-top, for that will better illustrate the phenomena which it is my wish to examine.” “If your object is the exercise of the body, let us spin the whip-top,” replied the vicar; “but if you wish to exercise the boy’s mind, I cannot object to your selecting the top best calculated to fulfil that desire.” Tom, having accordingly prepared his top, pulled the string, and set the wooden machine spinning on the floor. “Now, Tom, I will explain to you the reason of the top being able to sustain its vertical position. You have already learned, from the action of the sling, that a body cannot move in a circular path, without making an effort to fly off in a right line from the centre;[23] so that, if a body be affixed to a string, and whirled round by the hand, it will stretch it, and in a greater degree according as the circular motion is more rapid.” “Certainly,” said Tom. “The top, then, being in motion, all its parts tend to recede from the axis, and with greater force the more rapidly it revolves: hence it follows that these parts are like so many powers acting in a direction perpendicular to the axis; but, as they are all equal, and as they pass all round with rapidity by the rotation, the result must be that the top is in equilibrio on its point of support, or on the extremity of the axis on which it turns. But see, your top is down.” “And what is the reason,” asked Tom, “of its motion being stopped?” “I can answer that question, papa,” said Louisa; “is it not owing to the friction of the ground?”