104 THR NATURE STUDY COURSE. 



over a flame, and show it fall through by the heat-caused 

 enlargement of the ring. Lead pupils to the induction that 

 heat causes expansion of bodies whether solid or liquid. 

 Deduce practical applications, such as loosening the metallic 

 top of gem jars, setting buggy-tires, starting ground-glass 

 stoppers, etc. 



In Winter the Coldest Water is not at the Bottom of the 

 Lake. — Choosing a day when the thermometer stands about 

 32° F., set the bottle of colored water, referred to on the 

 preceding page, with the liquid standing high in the tube, on 

 the outside window-sill. The pupils may observe the liquid 

 descend until the thermometer falls to 39° F. ; then, if the 

 adjustments are all good, the water will begin to rise. 



Lead the pupils to see that water contracts as it cools to 

 39° F. When it gets colder than that it expands and, like ice, 

 will come to or stay at the surface. The surface layer is con- 

 verted into ice but the layer at the bottom does not get any 

 colder than 39° F. How does this affect the life of the fish 1 

 Why can no ice form on the lake until all the water in it has 

 cooled down to 39° F. 1 Lead the class to see that the Great 

 Lakes give off enormous quantities of heat and thus temper 

 the winter climate of adjoining regions of country. 



Freezing and Boiling Points. — Immerse the thermometer 

 bulb in a mixture of snow or broken ice and cold water. 

 Note its reading. 



Put the bulb in boiling water and note its reading. 



What is the temperature of water when it is passing from 

 the liquid to the solid form ? When passing from the boiling 

 liquid to vapor ? 



A study of the thermometer may be made here, and if 

 Fahrenheit and Centigrade scales are both to be had they 

 may be compared. 



