6o 
THE FAIRY-LAND OF SCIENCE. 
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 when they first see them, and at that 
moment they must have struck against the atmo- 
sphere, and even travelled some way through it, to 
become white-hot. In this way we have learnt that 
meteors burst into light at least 100 miles above the 
surface of the earth, and so the atmosphere must be 
more than 100 miles high. 
Our next question is as to the weight of our aerial 
ocean. You will easily understand that all this air 
Fig. 12. weighing down upon the earth 
must be very heavy, even though 
it grows lighter as it ascends. The 
atmosphere does, in fact, weigh 
down upon land at the level of the 
sea as much as if a 1 5-pound weight 
were put upon every square inch of 
land. This little piece of linen 
paper, which I am holding up, mea- 
A square inch of sures ex actly a square inch, and 
paper, as shown in the as it lies on the table, it is bearing 
a weight of 15 Ibs. on its surface! 
But how, then, comes it that I can lift it so easily ? 
Why am I not conscious of the weight? 
