130 GENERAL SCIENCE 



to multiply by one or the other of the above factors in 

 changing from one reading to the other. As it is, to change 

 degrees Centigrade to degrees Fahrenheit multiply by 1 

 and add 32. 



C X * + 32 = F 



To change degrees Fahrenheit to degrees Centigrade, 

 subtract 32 from the number of degrees and multiply by f . 



* (F - 32) = C 



Mercury is quite generally used in ordinary ther- 

 mometers, but since mercury freezes at about - 40 Centi- 

 grade and boils at about 350 Centigrade, mercury 

 thermometers cannot be used for extreme temperatures. 

 Alcohol thermometers are commonly used in cold cli- 

 mates. For temperatures above the boiling point of mer- 

 cury, other kinds of thermometers are used. 



EXERCISES 



1. Reduce 60 F. to Centigrade degrees. 



2. Reduce - 20 F. to Centigrade reading. 



3. Reduce - 40 C. to Fahrenheit. 



4. Mercury boils at 350 C. What will this temperature be in 

 Fahrenheit scale? 



5. Absolute zero is 273 C. Reduce this to Fahrenheit. 



Effects of Heat. The three main physical effects of 

 heat are expansion, fusion, and vaporization. There are 

 other effects, but they are mainly physiological and chem- 

 ical effects. 



Expansion. The first effect of heat on a body is to 

 cause its molecules to move faster. As they move faster 

 all the molecules strike against their neighbors with greater 

 force, pushing them farther and farther apart. This 



