MEASUREMENT OF TEMPERATURE 



27 



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change of temperature. He knew, too, that gases respond 

 far more rapidly to change of temperature than liquids 

 and solids and was thus led to his air thermometer. This 

 consisted of a glass tube of narrow bore, open at one 

 end and enlarged into a bulb at the other. The open 

 end of the tube was placed in a jar of liquid and the 

 bulb slightly heated. As the gas in the bulb cooled, 

 the liquid rose in the tube. Thus the relative tempera- 

 ture of the surrounding air could be told by the height 

 of the liquid in the tube. 



Mercury thermometers; Fahrenheit. Early in the 

 eighteenth century, 1714, Fahrenheit, of Danzig, Ger- 

 many, gave to the world his mercury 

 thermometer which is still used very ex- 

 tensively throughout the United States 

 and England. 



For the temperature of melting ice he 

 marked 32 and that of boiling water 

 212. The intervening distance he 

 divided into 180 parts or degrees. 



Centigrade. In 1742 Celsius, of Up- 

 sala, Sweden, devised the thermometer 

 known as the centigrade thermometer. 

 This thermometer is used almost exclu- 

 sively for scientific work in all countries, 

 and also for other purposes in countries 

 using the metric system. As the word 

 centigrade (centum : 100+ gradus : mark C enUg?'ade 6 'a n d 



-, N .. -'".,. Fahrenheit ther- 



or grade) suggests, the stem of this mometer. 





