13 



that they are too heavy to float. This growth is often aided by 

 the violent currents of air, which sometimes tumble and toss the 

 clouds about so that you can see the commotion from, the ground. 

 These currents blow one part- 

 icle against another, forming a 

 single drop from the collision 

 of two ; then still others are 

 added until the rain drop is so 

 heav}^ that it must fall. 



But sometimes the air cur- 

 rents are so rapid that the 

 drops are carried on up, higher 

 and higher, notwithstanding 

 the fact that the}' are heavy. 

 Then they may be carried so 

 high, and into air so cold, that 

 they are frozen, forming hail. 

 These "hailstones" cannot 

 sink to the ground until they 

 are thrown out of the violent 

 currents, when they fall to ^.—PkoLograph of a lightning flash. 

 the ground, often near the edge of the storm. 



Some hailstones are of great size ; you will find it interesting 

 to examine them. If you do this, notice the rings of clear and 

 clouded ice that are often to be seen. These are caused when 

 the hail, after forming, settles to a place where it melts a little, 

 then is lifted again by another current, growing larger by the 

 addition of more vapor. This continues until finally the ice ball 

 sinks to the ground. 



There is thunder and lightning in such storms. Few things 

 in nature are grander than these, and those who will watch the 

 lightning flash will see many beautiful and interesting sights 

 (Fig. 8). Sometimes the flash goes from cloud to cloud, again 

 from the cloud to the ground. No one knows exactly wh}' the 

 lightning comes ; but we do know that it is an electric spark, 

 something like that which one can often see pass from the trolley 

 to the wire of an electric car line. The main difference is that 

 the spark in a thunder storm is a powerful lightning bolt that 



