TH UNDER-S TO RMS 



163 



If a sharp point, such as a lightning rod, is present on 

 the object where the electricity tends to accumulate, it 

 allows the electricity to 

 pass off gradually before 

 enough accumulates to 

 cause damage. Light- 

 ning rods, however, 

 must be continuous 

 conductors and prop- 

 erly terminated in the 

 ground. 



80. Thunder-storms. 

 Often on a hot, sultry 

 summer afternoon large 

 cumulus clouds are seen 

 to rise and spread out 

 till they cover the sky. 

 The wind soon begins 

 to blow quite strongly 

 toward the cloud-covered area, the clouds moving in a 

 direction opposite to the surface wind. As the storm 

 clouds approach, a violent blast of wind, often called the 

 thunder squall, blows out from the front of the storm. 

 Soon flashes of lightning appear and thunder is heard. 

 As the storm comes nearer, the rain begins to descend 

 and for a short time, usually about half an hour, it rains 

 heavily. Then the clouds roll away and the sky becomes 

 clear with perhaps a rainbow to heighten the beauty of the 

 clearing landscape. 



Thunder-storms are caused by hot moist air rising over 

 certain areas and causing an updraft, which is increased 

 by the inflow and upward movement of air from the sur- 

 rounding regions. The condensation of the moisture in the 

 rising air quickly forms clouds, and these become charged 



TREE COMPLETELY SHATTERED BY A 

 STROKE OF LIGHTNING. 



