THE AERIAL OCEAN IN WHICH WE LIVE. 63 
should have never suspected would be useful to us in 
this way, have let us into the secret of the height of 
the atmosphere. These bodies are the meteors, or 
falling stars. 
Most people, at one time or another, have seen what 
looks like a star shoot right across the sky, and dis- 
appear. On a clear starlight night you may often see 
one or more of these bright lights flash through the 
air; for one falls on an average in every twenty min- 
utes, and on the nights of August 9th and -November 
1 3th there are numbers in one part of the sky. These 
bodies are not really stars ; they are simply stones or 
lumps of metal flying through the air, and taking fire 
by clashing against the atoms of oxygen in it. There 
are great numbers of these masses moving round and 
round the sun, and when our earth comes across their 
path, as it does especially in August and November, 
they dash with such tremendous force through the 
atmosphere that they grow white-hot, and give out 
light, and then disappear, melted into vapour. Every 
now and then one falls to the earth before it is all 
melted away, and thus we learn that these stones 
contain tin, iron, sulphur, phosphorus, and other sub- 
stances. 
It is while these bodies are burning that they look 
to us like falling stars, and when we see them we know 
that they must be dashing against our atmosphere. 
Now if two people stand a certain known distance, 
say fifty miles, apart on the earth, and observe these 
meteors and the direction in which, they each see them 
fall, they can calculate (by means of the angle between 
the two directions) how high they are above them 
