SOME USES OF A THERMOMETER 



The tube is then removed from the boiling water, and after 



cooling for a few minutes, it is placed in a vessel containing 



fi nely chopped ice ( Fig. i o). The mercury 



column falls rapidly, but finally remains 



stationary, and at this level another 



scratch is made on the tube and the point 



is marked 32. The space between these 



two points, which represent the tempera- 

 tures of boiling water and of melting ice, 



is divided into 180 equal parts called de- 

 grees. The thermometer in use in the 



United States is marked in this way and 



is called the Fahrenheit thermometer 



after its designer. Before the degrees 



are etched on the thermometer the open 

 end of the tube is sealed. 



The Centigrade ther- 

 mometer, in use in foreign 

 countries and in all scien- 

 tific work, is similar to the Fahrenheit except 

 that the fixed points are marked 100 and o, 

 and the interval between the points is divided 

 into 100 equal parts instead oTf into 1 80. 



The boiling point of water is 212 F. or 

 100 C. 



The melting point of ice is 32 F. or O C. 



FIG io. Deter- Glass thermometers of the above type .are 



mining the lower 



fixed point of a the ones most generally used, but there are 



thermometer. mail y different types for special purposes. 



7. Some Uses of a Thermometer. One of the chief values 



of a thermometer is the service it has rendered to medicine. 



If a thermometer is held for a few minutes under the tongue 



of a normal, healthy person, the mercury will rise to about 



FiG. 9. Determining one 

 of the fixed points of a 

 thermometer. 



