HEAT 69 



our sense. We must not judge of the nature of heat by 

 this single effect, for it is only one of many different 

 effects. It is important, in order to understand the 

 further study of this chapter, that we fix firmly in 

 mind the idea that heat is a form of energy the energy 

 of molecular motion. 



76. Cold. Cold means simply the absence of heat. 

 Since heat is molecular energy, and the molecules of 

 every mass are in motion, it follows that no body has 

 absolutely no heat. Thus complete cold is unknown. 

 We use the word cold to express a condition of less heat 

 than some other substance has. 



77. Temperature. Temperature is the condition of 

 a body with regard to the intensity of its heat. If a 

 body is warmer than another, we say that it has a higher 

 temperature; if colder, we say its temperature is lower. 



Care must be taken to avoid calling temperature the 

 " quantity of heat " of a body. A cupful of water might 

 have a higher temperature than water in a kettle ; but 

 at the same time the kettleful would have a greater 

 quantity of heat, because there is so much more water. 

 Temperature is the average heat of each particle, while 

 quantity of heat is the average of each particle multi- 

 plied by the number of particles. 



78. The Thermometer. The thermometer is a device 

 for measuring temperature. It does this by expressing, in 

 degrees, how much warmer or colder a body is than some 

 other substance taken as a standard. Two thermometers 

 are in common use, the Centigrade and the Fahrenheit. 



