The Upper Air 107 
wagons—convinced that the world was coming to an end. 
The true, material nature of meteors was first satisfactorily 
proved by the German physicist, Chladni (1756-1827), who 
demonstrated that they are chunks of rock or iron that are 
flying around in the unfathomable void of outer space. 
When they approach the earth they are attracted to it with 
velocities up to 42 miles per second. Upon striking the upper 
air they are heated to incandescence by the friction of the 
air. If they are iron their outer surface is melted and be- 
comes white hot. 
Most meteors are only the size of grains of sand, and soon 
burn up when they strike the upper air. Others are bigger, 
large enough to reach the surface of the earth or ocean be- 
fore being burned up. They have been found in all sizes up 
to many tons on the surface of the dry land, and small ones 
are continually being found in the clays and ooze dredged 
from the deep ocean floor. When meteors flash into our at- 
mosphere they give off momentarily a bright light, like stars 
that suddenly dart across the sky and disappear. They are 
often spoken of as “shooting stars” although of course they 
are not stars at all. | 
The brighter ones are called fireballs or bolides. Sometimes 
they fade out quietly, at other times they explode violently 
like a rocket and the report may follow many seconds later. 
Occasionally they are bright enough to light up the entire 
sea for miles around. Some are visible even in full daylight. 
Other meteors leave luminous trails in the sky that are vis- 
ible long after the meteor itself has disappeared. 
Meteors usually occur in sporadic bursts—several at a 
time. This is because in their lonely wandering through 
space for millions of years they tend to pick up companions 
