“It is an instrument of great antiquity,” replied his father: “its invention is generally ascribed to Ctesebes of Alexandria, who lived about 120 years before Christ; but the principle of its action was not understood for ages after its invention. The ancients entertained a belief that ‘Nature _abhorred_ a vacuum;’ and they imagined that, when the piston ascended, the water immediately rushed forward to prevent the occurrence of this much dreaded vacuum. In the seventeenth century a pump was constructed at Florence, by which it was attempted to raise water from a well to a very considerable altitude, but it was found that no exertion of this machine could be made to raise it above 32 feet from its level. This unexpected embarrassment greatly puzzled the engineer, until Galileo suggested that the pressure on the water below must cause its ascent into the pump, and that, according to this theory, when it had risen 32 feet, its pressure became equivalent to that of the atmosphere, and could, therefore, not rise any higher; and as they did not, at that time, understand the construction of the piston valve, the design was abandoned. It is now time to conclude your lesson. To-morrow I hope we shall be able to enter upon the subject of THE KITE.” ----- Footnote 38: A scientific friend observed to the author, that, as the globe possesses less surface than any other figure of equal capacity, it is of all forms that which is best calculated to allow the closest approximation of the particles of soap and water; and as there must exist amongst such particles a strong cohesive tendency, after having been forcibly stretched out, as it were, by the air blown into the bubble, it follows that, did no other cause operate, the bubble would assume the spherical form. Footnote 39: Not exceeding the two millionth part of an inch. Footnote 40: Line 171. ------------------------------------------------------------------------ [Illustration: Two boys causing havoc by upsetting a washerwoman.] CHAPTER XIII. _The Kite.--Its construction.--The Tail.--An Author’s meditations among the catacombs of Paternoster Row.--Works in their winding sheets.--How Mr. Seymour strung puns as he strung the Kite’s tail.--The Vicar’s dismay.--The Weather, with the hopes and fears which it alternately inspired.--Kites constructed in various shapes.--The figure usually adopted to be preferred.--The flight of the Kite.--A philosophical disquisition upon the forces by which its ascent is accomplished.--The Tail.--A Discourse on the theory of flying.--The structure and action of the wings of birds.--A series of kites on one string.--A Kite Carriage.--The Messenger.--The causes and velocity of wind explained._