THUNDER-CLOUDS. 2 6 7 



If clouds are formed, which, being water 

 gathered together in the atmosphere, can carry 

 electricity, and if they are surrounded by non- 

 conducting air, the electricity, which was already 

 present in their neighbourhood, gradually collects 

 upon their surfaces, just as takes place with any 

 other insulated conductor, to which electricity is 

 imparted. These charges, however, are generally 

 drawn off to the earth by rain or snow, without 

 any very striking effect. But, if the mass of 

 clouds is very large, and the gathering of the 

 water within them takes place very quickly and 

 plentifully, then their inner body becomes in a 

 short time a most excellent conductor, and may 

 suddenly send up to the surface of the cloud elec- 

 tricity enough in amount, and condensed to such 

 a degree, that a powerful discharge must follow — 

 a flashing of the spark to another cloud, or, 

 perhaps, to the surface of the earth, through the 

 layer of air between — before the charge can be 

 gradually let off by the fall of rain. 



The lightning is commonly accompanied by a 

 loud noise,— the Thunder. It is the result of the 

 shock, which is occasioned by the flash in bursting 

 through the air, and is owing to the same cause 

 as is the snap of the smallest electric spark. The 

 long resounding roll of the thunder arises from the 

 echo of the first single crash thrown back from 

 hills and heights, and from the clouds themselves. 



