130 SCIENCE OF COMMON THINGS. 



Heat has no weight How heat is measured. What is cold ? 



SIS Has heat any perceptible weight? 



No ; if we balance a quantity of ice in a delicate 

 scale, and then leave it to melt, the equilibrium will 

 not be in the slightest degree disturbed. If we substi- 

 tute for the ice boiling water or a red-hot iron, and leave 

 this to cool, there will be no difference in the result. 



813 What important property distinguishes heat from all other agents 

 or substances in nature f 



The property of passing through and existing in all 

 kinds of matter at ail times / heat is everywhere present, 

 and every body that exists contains it without known 

 limit. 



814 Has ice heat ? 



Yes, large quantities of it. Sir Humphrey -Davy, by 

 friction, extracted heat from two pieces of ice, and 

 quickly melted them, in a room cooled below the freez- 

 ing point, by rubbing them against each other. 



815 How do we measure the quantity of heat in different bodies, or judge 

 of its effects ? 



Only by the change in hulk or appearance which 

 different bodies assume, according as neat is added or 

 subtracted. 



810 According to what law does heat diffuse or spread itself 'f 



Heat diffuses or spreads itself among neighboring 

 bodies until all have acquired the same temperature / 

 that is to say, until all will similarly affect the thermo- 

 meter. 



817* Why does a piece of iron thrust into burning coals become hoi 

 among them f 



Because the heat passes from the coals into the iron 

 until the metal has acquired an equal temperature. 



818 What is cold? 



Cold is a relative term expressing only the absence 

 of heat in a degree ; not its total absence, for heat 

 exists always in all bodies. 



810 When the hand touches a body having a higher temperature than 

 itself, why do we call it hot ? 



Because on account of the law that heat diffuses 



