SOME USES OF A THERMOMETER 



scratch is made on the tube to indicate the 

 point to which the mercury rises when the 

 bulb is placed in boiling water, and this 

 point is marked 212. The tube is then re- 

 moved from the boiling water, and after 

 cooling for a few minutes, it is placed in a 

 vessel containing finely chopped ice (Fig. 

 9). 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 be- 

 tween these two points, which represent 

 the temperatures of boiling water and of 

 melting ice, is divided into 180 equal parts FlG 8 

 called degrees. The thermometer in use 

 in the United States is marked in this 



Determining 

 one of the fixed points 

 of a thermometer. 



way and is called the Fahrenheit thermometer after its designer. 

 The Centigrade thermometer, in use in foreign countries 

 and in all scientific 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 of into 180. 



The boiling point of water is 212 F. or 100 C. 

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

 Glass thermometers of the above type are the 

 ones most generally used, but there are many 

 different types for special purposes (Fig. 10). 



Some uses of a thermometer. One of the 

 chief values of a thermometer is the service it has 

 rendered to medicine. When a thermometer is 

 FIG. 9. Deter- held for a few minutes under the tongue of a 

 norma ^ healthy person, the mercury rises to about 



thermometer. 98.4 F. When the temperature of the body 



CI.ARK INTRO. TO SC. 2 



