HEAT 



129 



212 



stands is marked as the freezing point. This point is called 

 zero on the Centigrade scale and thirty-two degrees on 

 the Fahrenheit scale (Figure 111). To locate the boiling 

 point of water, place the tube in boiling water, or better, 

 the steam immediately over boiling 

 water. The point at which the mer- 

 cury now stands is marked 100 on the 

 Centigrade scale and 212 on the Fah- 

 renheit. The space between these two 

 fixed points is divided into one hun- 

 dred equal parts for the Centigrade 

 thermometer and 180 equal parts for 

 the Fahrenheit scale. In scientific 

 work the Centigrade scale has come 

 into almost universal use and in many 

 countries it is the only thermometer 

 used. It is unfortunate that the 

 Fahrenheit thermometer ever came 

 into use in our country as a weather 

 bureau instrument, since its scale is so 

 cumbersome. It must be remembered 

 that the two thermometers differ only 

 in their scales (Figure 112). 



The difference between the freez- 

 ing point and the boiling point on 

 the Centigrade scale is 100 degrees and on the Fahrenheit 

 scale 180 degrees. 



180 F. equal 100 C. 



18 F. equal 10 C. 



1 F. equal f C. 



or 1 C. equal f F. 



Were it not for the fact that the freezing point is marked 

 32 on the Fahrenheit scale, it would only be necessary 



-40 



FIG. 1 12. Compari- 

 son of the Fahrenheit 

 and Centigrade Ther- 

 mometer Scales. 



