142 ELEMENTARY GENERAL SCIENCE CHAP. 



or one degree Fahrenheit is equal to five-ninths of a degree 

 Centigrade. 



100 C degs. = 180 F degs. ; /. 5C.=9F. .'. C.=F. orF.=jj C. 



In converting Fahrenheit readings into Centigrade degrees, we 

 must subtract 32 (because of what has been said of the freezing 

 point on the former scale) and multiply the number thus obtained 

 by 5 and divide by 9. To change from Centigrade to Fahrenheit, 

 multiply the former reading by 9 and divide by 5 and add 32 to 

 the result. 



EXAMPLE. What temperature on the Fahrenheit scale 

 corresponds to 20 C ? 



ANSWER. 20 C is 20 C degs. above temperature of melt- 

 ing ice, i.e. 20 xf Fahr. degs. above 32 F = (36 + 32) F = 

 68 F. 



When it is necessary to refer to temperatures lower than the 

 freezing point of water a minus sign is placed before the tem- 

 perature, thus three degrees below the freezing point of water 

 on the Centigrade scale is written - 3 C. 



Distinction between Heat and Temperature. Temperature 

 is not heat. It is only a state of a body, for the body may be 

 cold one minute and hot the next. A hot body is one at a high 

 temperature, a cold body one at a low temperature. If a hot 

 body and a cold body be brought into contact there is a passage 

 of heat from the hot one to the cold until they are both of the 

 same degree of hotness or coldness. Now in this last sentence 

 substitute " at a high temperature" for "hot," and "at a low 

 temperature" for "cold," and we shall see our way to a defini- 

 tion of temperature ; thus, if a body at a high temperature and 

 one at a low temperature be brought into contact there is a passage 

 of heat from the former to the latter until they are both at the 

 same temperature. Hence, we can define temperature as a 

 condition of bodies that determines which of two bodies 

 when placed in contact will part with heat to the other. 

 Temperature may also be defined as intensity of heat. 



Evidently temperature is analogous to the level of water, for 

 we have learnt that if two cisterns containing water at different 

 levels be put in connection there will be a flow of water from the 

 one where the water stands at the higher level to the other until 

 they assume the same level. 



