122 The Sky 
HOW IS LIGHTNING PRODUCED? 
From their attempts. to explain the wide variety of elec- 
trical phenomena, both those that occur naturally and those 
that can be produced in the laboratory, physicists have come 
to believe that electricity is made up of small particles called 
electrons. Electrons which are bound in systems with other 
kinds of elementary particles make up atoms of matter; but 
when free to roam for themselves they produce electric cur- 
rents. When we speak of positive electricity, they say, we 
really mean the absence of electrons. Negative electricity is 
the presence of electrons. Electrons are subject to a compel- 
ling tendency to get to places where they are scarce. In the 
swirling clouds of a thunderstorm, electrons may be sepa- 
rated systematically from certain parts of clouds and accu- 
mulated in other portions. When these accumulations of elec- 
_trons build up too high, there is a sudden discharge between 
the clouds or between a cloud and the earth as the electrons 
make a dash to restore a more equitable distribution of them- 
selves. Such a discharge is a stroke of lightning. 
One frequently experiences a sudden shower of rain di- 
rectly following a lightning stroke. Contrary to a popular 
misconception, it is not the lightning that produces the extra 
rain, but the rain that produces the lightning. In falling, 
raindrops accumulate electric charges from the surrounding 
air in much the same way a cat’s fur accumulates charges 
when brushed. The raindrops carry these charges to the 
ground and in this way transport electricity from one place 
to another, building up inequalities in the distribution of 
electricity which are evened out by lightning bolts or slower 
brush discharge. The apparent reversal of cause and effect in 
time occurs because the rain takes so much longer to fall on 
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