This section is from "The American Cyclopaedia", by George Ripley And Charles A. Dana. Also available from Amazon: The New American Cyclopędia. 16 volumes complete..

**Centigrade Scale**, the 100 parts, named grades or degrees, adopted particularly by the French for the thermometer. It was devised in 1742 by Celsius, professor at Upsal, the limits of the division into 100° being the boiling and freezing points of water, though the scale is made to extend to convenient lengths below and above these points. In Fahrenheit's scale, the freezing point being 32° and the boiling point 212°, 180° include the same range as 100° of the centigrade thermometer. The ratio of one degree of Fahrenheit to one of the centigrade is therefore the same with that of 5 to 9. But as the zero point of the Fahrenheit thermometer is 32° below the freezing point, which is the zero point of the centigrade, this number must be added to the results obtained from the ratio above stated. Thus, if the degree on the Fahrenheit scale which corresponds to 15° centigrade is to be found, 15 must first be multiplied by 9 and the product divided by 5; to 27, the quotient obtained, 32 must be added, and the sum, 59, will be the degree on the Fahrenheit scale required.

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