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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. 1907 edition. Excerpt: ... scale is constructed by first placing the instrument under a bell glass with several pieces of wet blotting paper near but not touching the strip. The long, narrow strip does not change its length, but is bent one way or the other by the swelling or shrinking of the piece which is glued crosswise. The hygroscopic strip will straighten out or even curve in the opposite direction when submitted to the influence of moisture, and after the lapse of six or eight hours the glass is removed and a pencil mark is made on the card at the point of the index, which will represent 100 degrees, or the point of saturation. The instrument is allowed to assume the normal position by drying it in the open air, after which it is again placed under the bell glass with a dish of calcium chloride and allowed to remain five or six hours. The calcium chloride removes the moisture and causes the cross-grained side to shrink and thus curve the strip considerably. It now indicates the maximum dryness of the air, and a mark is made at the point of the index, indicating zero. The spaces between zero and saturation should now be divided into ten equal spaces, and each space may be subdivided into ten spaces, each representing one degree. These lines should be neatly made with a drawing pen. Every tenth graduation should be extended a little and numbered; the entire scale being numbered from 0 to 100, i, e., 0, 10, 20, 30, etc. This instrument is not intended to accurately show the exact amount of moisture, as is the case with the more elaborate hygrometers, but to afford a simple means of showing the ever-varying state of the air. MERCURIAL BAROMETER The variations of atmospheric pressure are shown by the barometer. The pressure of the air in round numbers is 15 pounds per...
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Product details

  • Paperback | 68 pages
  • 189 x 246 x 4mm | 141g
  • Rarebooksclub.com
  • Miami Fl, United States
  • English
  • black & white illustrations
  • 1236628969
  • 9781236628961