Heat 



FIG. 43. Will the hot ball go through the ring? 



the thermometer like everything else expands (swells) 

 when it becomes warm. It is shut in tightly on all 

 sides by the glass, except for the little opening into the 

 tube above. When it expands it must have more room, 

 and the only space into which it can move is up in the 

 tube. So it rises in the tube. 



Water will do the same thing. You can make a sort 

 of thermometer, using water instead of mercury, and 

 watch the water expand when you heat it. Here are 

 the directions for doing this : 



