Heat 



117 



FIG. 57. Does the heat travel faster through the iron or through the glass? 



inches long. With sealing wax or candle grease stick three 

 ball bearings or pieces of lead, all the same size, to each rod, 

 about an inch apart, beginning 2 inches from the end. Hold 

 the rods side by side with their ends in a flame, and watch 

 the balls fall off as the heat comes along through the rods. 

 The heat that first melts off the balls beats. 



What really happens down among the molecules 

 when the heat travels along the rods is that the mole- 

 cules near the flame are made to move more quickly; 

 they joggle their neighbors and make them move faster ; 

 these joggle the ones next to them, and so on down the 

 line. Heat that travels through things in this way is 



