A First Course of Practical Science; With Full Directions for Experiments and Numerous Exercises

A First Course of Practical Science; With Full Directions for Experiments and Numerous Exercises

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This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1904 edition. Excerpt: ...the hot wire would weigh less because you have cut a bit off. And if you think a little further you will see that when any substance has expanded, any volume of it is lighter than the same volume of it before expansion. This fact is very important, and I want you to remember it. There are one or two practical consequences of things expanding which are interesting. When a blacksmith puts a new tyre on a wheel he makes the tyre hot, so that it slips easily on to the wheel; then, on cooling, the tyre contracts, gripping the wheel firmly and securely. You may have noticed, too, a little space left between each couple of adjoining railway rails: this is to give room for their expansion under the summer sunshine. If the little space were not left like this, the rails would arch in expanding, and a serious accident might happen. Take the temperature of the air some distance above the fire in a grate. The fire has heated this air, and so it expands. The expanded air, as you will know, is lighter than an equal volume of the cool contracted air. The direction of the smoke shows you that the heated air is risi lg. Why? For the same reason that a piece of cork would rise if let go under water. But think: when the cork rises from one position to the next, the water rushes in to take its place. Does other air rush in to take the place of the hot air which has risen? Put a piece of paper on the floor at the bottom of the door: the paper is blown away. This shows you that air is rushing in to take the place of the hot air which is rising. Take the temperature of this inrushing air at the bottom of the door: notice that it is much colder than the uprising air over the fire. The inrush of air is spoken of as a draught. What the fire is doing with respect to the...show more

Product details

  • Paperback | 50 pages
  • 189 x 246 x 3mm | 109g
  • Rarebooksclub.com
  • Miami Fl, United States
  • English
  • black & white illustrations
  • 1236487958
  • 9781236487957