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give no further explanation than that it rises " because it is heated." 

 The fact that heated air "goes down" in some cases may be referred to. 

 (The general subject of why things float when immersed in liquids or 

 gases heavier than they are may be taken up.) 



HEAT EXPANDS SOLIDS. 



The question may now be asked of the pupils: Does heat expand 

 solids? They will be ready to say that they think that it does, and now 

 comes the opportunity of having them devise a means of proving it. If, 

 unaided, anyone of the class can invent such apparatus the results will 

 be excellent. The following are some simple forms of apparatus used 

 to illustrate expansion of solids. A metal ball just passing through a 

 metal ring at the ordinary temperature of the room, will not pass when 

 heated, and will pass more readily when the ring is heated. An iron or 

 other metal bolt nicely fitting into a hole in another piece of metal 

 may be used in the same way. A simple apparatus can be made which 

 will show expansion in rods of various metals, or of various forms such 

 as poker, stove lid, gas pipe, etc. Two heavy blocks of wood are used 

 to support the object. On one side of one block is nailed a strip pro- 

 jecting above the top of the block. One end of the object (iron poker 

 for example) is supported by this block, the end of the poker being 

 pushed firmly against the projecting strip, the other end of the poker is 

 supported by the other block, the end projecting beyond the block. 

 When the poker is heated the strip prevents the expanding poker from 

 pushing in that direction, thus the whole of the movement is shown at 

 the free end. As the expansion is very small, it may be made conspic- 

 uous by use of an indicator, made as follows: On a small upright sup- 

 port 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 expands the long end as a pointer passes over 

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

 end of the lever is very shorv, 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 alcohol 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 for them. 



The Fern. 



Though the fern is one of the most common of our house-plants, yet 

 its life history is not generally known. There are two stages in its life, 



