102 



APPLIED -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. 



FIG. 61. Cen- 

 tigrade and 

 Fahrenheit 

 Scales. 



heit is 

 letter O. 



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 

 freezing points, together with conversion for- 

 mulas for use in changing readings from one 

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

 denoted by the letter F. and Centigrade by the 



Boiling Point 



Fahrenheit Scale 212 



Centigrade Scale 100 



To convert Fahrenheit to Centigrade: 

 5(F-32) 



Freezing Point 



32 







= C 



To convert Centigrade to Fahrenheit : 



- C + 32 = F 



o 



* For a description and illustration of the pyrometer see Chapter 

 XV. 



