The Century Volume 21

The Century Volume 21

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This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1881 edition. Excerpt: ...when suspended in the water. In the tank are suspended two standard thermometers, one close to the glass, and the other on the carrier. This carrier consists of a brass frame, like the dasher of a churn, and filled with holes ranged around the edge; each hole is numbered, and the glasses are suspended in these holes by means of a clamp, a duplicate plate on top of the tank carrying corresponding numbers to guide the operator in his work. The carrier is suspended freely in the tank, and may be turned around by means of a hand-crank, the revolution of the carrier bringing each glass into view through the slit in succession. The tank is filled with water by means of pipes from a domestic hot and cold water apparatus (an improvement on the English method of pouring in hot water from a tea-kettle), and when the water is brought to 90 Fahr., and properly churned, the glasses are suspended in it and slowly examined, one at a time, at least twice. The examination is made by looking through a microscope, and the difference between its record and that of the standard thermometer is noted in tenths of a degree. The temperature of the water is then slowly raised to 110 Fahr., and each thermometer is examined minutely on every fifth degree, and the mean of all its errors is recorded. The Bureau then gives a certificate, saying that the glass (known by the maker's name and number) is correct on every fifth degree, or is in error above or below these points so much, in tenths of a degree. This certificate is then the measure of the commercial value of the glass. It enhances the price, and gives the purchaser a positive assurance of its value and a guide to the habits of that particular instrument. It sometimes happens, for reasons beyond the control of...show more

Product details

  • Paperback | 648 pages
  • 189 x 246 x 33mm | 1,139g
  • Rarebooksclub.com
  • United States
  • English
  • black & white illustrations
  • 1236763149
  • 9781236763143