“I cannot imagine what you are about, papa;--‘Light the candle, and then blow it out!’--but it still smokes, shall I put the extinguisher over it?” “By no means; give it to me, and observe what will happen when I carry it round the edge of the dish.” “The smoke goes to the centre,” exclaimed Tom. “Showing, thereby, the existence of a current towards the water-plate, or island; in consequence of the air above it having been heated, and therefore rarefied. This explains in a very satisfactory manner, a fact which may be constantly observed in our own climate, viz. a gentle breeze blowing from the sea to the land in the heat of the day. Upon the same principle it is, that most of the winds in different parts of the globe may be readily accounted for.”(42) “I suppose,” said Tom, “that the air must rush with great velocity, in order to produce wind.” “A very general error prevails upon this subject,” replied his father; “the rate of motion has been greatly exaggerated. In a brisk gale, even, the wind does not travel with such velocity, but that it may be easily traced by the eye; and the sailor is able to watch its progress by the ripple which it produces on the sea.” “Has, then, the rate of its motion ever been estimated?” asked Louisa. “When its velocity is about two miles per hour, it is only just perceptible. In a high wind, the air travels thirty or forty miles in the same period. In a storm, its rate has been computed as being from sixty to eighty miles. It has also been ascertained, by experiment, that the air, as it rushes from a pair of blacksmith’s bellows, has not a velocity above that of five and forty miles in the hour.” “At what rate should you think the air travelled this morning, when we flew our kite?” enquired Louisa. “I should think at about five miles an hour, for it was a pleasant but gentle breeze.” ----- Footnote 41: The author has been thus minute, in order to afford his young friends clear directions for constructing a kite, and which, as far as he knows, are not to be found in any work hitherto published; and he will also avail himself of this opportunity to state, that the thin glazed linen of various colours, commonly known to haberdashers by the name of lining, has been found to be the best material as a covering for the kite. It is not only more durable than paper, defying the most boisterous wind, but superior to it as being secure from the effects of a shower of rain. Footnote 42: Those readers, who are inclined to enter more deeply into the subject, may consult, with advantage, a memoir on the kite, by Euler, published in the Transactions of the Academy of Berlin for the year 1756. Footnote 43: See p. 60. Footnote 44: From associations of an interesting nature connected with the residence of the author’s children. Footnote 45: Transactions of the Society for the Encouragement of Arts, vol. xli.; and Miss Edgeworth’s Harry and Lucy, vol. iv. p. 288.