102 



. . . JLPPUE.D .SCIENCE 



heit and Centigrade thermometers, namely, that substances 

 expand with an increase and contract with a 

 decrease of temperature. In the measurement 

 of heat in stoves and furnaces where the tem- 

 perature exceeds 900 F. an instrument called 

 a pyrometer* is used. 



103. Relation between Fahrenheit and Centi- 

 grade Scales. While all temperature measure- 

 ments in American and English shops are 

 expressed according to the Fahrenheit scale ; 

 it is often necessary to change the Fahrenheit 

 into the Centigrade readings. Below is given 



a comparison of the two at the boiling and 

 FIG. 61. Cen- . 



tigrade and freezing points, together with conversion for- 



ScaJes enh0lt mu ^ as f r llse m changing readings from one 

 standard to the other. (Figure 61.) Fahren- 

 heit is denoted by the letter F. and Centigrade by the 

 letter C. 



Boiling Point 



Fahrenheit Scale 212 



Centigrade Scale 100 



To convert Fahrenheit to Centigrade: 



5 (F - 32) 



Freezing Point 



32 







To convert Centigrade to Fahrenheit 



- C + 32 = F 

 .5 



* For a description and illustration of the pyrometer see Chapter 

 XV. 



