Page:International Library of Technology, Volume 93.djvu/33

 12. Absolute Temperature. — The freezing point was chosen as the zero point of the centigrade scale. When the Fahrenheit scale was invented, the zero point of the thermometer was placed 32° below the freezing point, as that was the lowest temperature that could then be obtained, and it was supposed that it was impossible to obtain a lower one. From the results of experiments and from calculations, however, it has been concluded that at 460° F. below zero, or 492° F. below the freezing point, there is absolutely no vibration of the molecules and consequently no heat. This is therefore called the absolute zero, and all temperatures reckoned from this point are called absolute temperatures. Absolute zero has never been reached, the lowest recorded temperature being in the neighborhood of —400° F.

13. Reckoning Absolute Temperature. — Absolute temperature may be reckoned either on the Fahrenheit or on the centigrade scale. Between 0° absolute and 0° F. there are 460 Fahrenheit degrees; between 0° absolute and the freezing point there are 460 + 32 = 492°; while between 0° absolute and the boiling point there are 460 + 212 = 672°. Between 0° absolute and 0° C. there are 273i centigrade degrees. Absolute Temperature, Fahrenheit. — If the absolute temperature of a body, in degrees Fahrenheit, is given, its temperature on the ordinary Fahrenheit thermometer can be found by subtracting 460 from the absolute temperature. If the absolute temperature is less than 460, subtract it from 460, and the result will be the temperature below zero on the Fahrenheit thermometer.

The absolute temperature of a body, in degrees Fahrenheit, may be found from its Fahrenheit temperature by adding 460 to it, when the thermometer reading is above zero; if the thermometer reading is below zero, subtract the reading from 460. Thus, 150° F. = 150 + 460 = 610° F., absolute; - 23° F. = 460 - 23 = 437° F., absolute.

Absolute Temperature Centigrade. — To find the absolute temperature of a body from its centigrade temperature, add the centigrade temperature to 273⅓ when it is above zero,