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FIRST TEAR SCIENCE 



to each of the knobs and extend it vertically two or three inches above 

 the knob. Start the machine. Do sparks now jump across between 

 the knobs? Why are houses provided with lightning rods? 



Fig. 75. 



About the middle of the eighteenth century, Benjamin 

 Franklin proved by his notable kite experiment that 



lightning was simply an elec- 

 trical discharge between the 

 clouds and the earth, or be- 

 tween different clouds. This 

 discharge is similar to that 

 which takes place on an elec- 

 trical machine. The electricity 

 in the clouds attracts as near as 

 possible the opposite kind of 

 electricity on the earth's surface 

 and tends to hold it accumu- 

 lated on high objects. If the attraction is sufficient, the 

 electricity discharges between the cloud and the object, 

 and we say the object was struck by lightning. 



A FLASH OF LIGHTNING. 



Showing it takes different paths 

 of least resistance. 



