432 ] Understanding the Weather 



sure between these two parts of the cloud becomes powerful 

 enough to break through the air so they can join each other, a 

 tremendous spark lightning is created. 



"LIGHTNING" IN A STORAGE BATTERY 



If you are interested in things electrical, and have some 

 simple equipment, you probably know how to give your child a 

 dramatic illustration of how lightning is formed and thunder 

 too. All you need do is connect the positive and negative poles of 

 a storage battery with a piece of wire. As the youngster looks on, 

 he will see how quickly a spark is created there, caused by the 

 negative particles (electrons) leaping toward the positive pole. 

 He will hear, too, a crackling sound accompanying the spark. 



In just the same way the giant sparks that flash across the sky 

 produce a crackling sound of tremendous volume. We call it 

 thunder. 



FORKED LIGHTNING AND OTHER KINDS 



Lightning comes in different forms. The most common type 

 is forked lightning with a brilliant zigzag flash, as the electrical dis- 

 charge takes the path of least resistance an irregular one through 

 the air. A second kind, "sheet" lightning, is caused by a flash 

 hidden in the clouds which brightly but briefly lights up a whole 

 cloud or a sheet of rain. 



Finally, there is "heat" lightning a description we often give 

 to a sudden lighting of the atmosphere that appears near the hori- 

 zon though no thunderclouds are in sight. Heat lightning is usual- 

 ly explained as the reflection of lightning flashes below the horizon 

 by the hazy air within our range of vision. It is appropriately 

 named "heat lightning," as we encounter it during hot, muggy 

 weather. 



WHEN LIGHTNING is DANGEROUS 



Though we want to reassure a child on the subject of 

 lightning, we must not fail to let him know the circumstances 

 under which it can be a real danger. Most flashes are from one 



