"The father of the righteous shall greatly rejoice; and he that begetteth a wise child shall have joy of him."—Proverbs xxiii.
CHAPTER XXXVIII.
810. Why does a humming-top make a humming noise?
Because the hollow wood of the top vibrates, and the edges of the hole in its sides strike against the air as it spins; the air is thereby set in vibration.
811. Why does a peg-top hum less than a humming-top?
Because, being a solid body of wood, and having no hole in its sides, its particles are not so easily thrown into vibration; consequently it does not so readily impart vibrations to the air.
812. Why does a peg-top sometimes hum, and at other times not?