S6 NATURE STUDY 



free eud. As the expansion is very small, it may be made con- 

 spicuous by use of an indicator, made as follows: On a small 

 upright support high enough to stand just behind the free end of 

 the poker, place a card with degrees of a circle marked on it. At 

 the center of the circle fasten a pin or small nail on which turns 

 as a pivot a slender strip of wood as a lever. If the short end of 

 the lever is placed against the end of the poker when it 

 pands the long end as a pointer passes over the gradua- 

 ted circle, giving a magnified view of the expansion. If one end 

 of the lever is very short, and the other long, a small amount of 

 expansion may be detected. On this simple apparatus many 

 objects may be tested. The heating may be accomplished by al- 

 cohol lamps, or a row of candles. 



If two strips of different metals are riveted together, and 

 heated, the unequal expansion of the metals will cause the double 

 strip to bend. Iron and copper are good selections. 



Illustrations of effects of expansion of solids may be found if 

 pupils are set to looking out tor them. 



