TEMPERATURE SENSATIONS 



51 



school. Keep a record of the temperature and you can 

 tell the hot days and the cold days, without trusting to 

 your memory. A record is to be trusted. See Section 

 69. 



Another practical application of the unequal expan- 

 sion of metals is the dial thermometer. You have all 

 seen thermometers which have a hand moving over what 

 appears very much like the face of a clock. In the place 

 of the hours, however, the face is marked into divisions 

 which are numbered usually from zero to a- hundred or 

 more. The word "Fah- 

 renheit" generally i s 

 printed upon the face of 

 the instrument. The 

 movement of the hand 

 is caused by the winding 

 up, or the unwinding, of 

 a spiral, due to the un- 

 equal expansion of the 

 two metals of which it is 

 composed. The illustra- 

 tion shows the spiral but 

 does not show the two 

 metals. Both metals are 

 quite thin and are fas f - 

 ened together their entire length just as we learned the 

 heat regulator was made. 



We should not depend upon our feelings in regard 

 to temperature. If we have been exercising we are warm 

 Cut supplied by the Standard Thermometer Co. 



