6 4 
THE FAIRY-LAND OF SCIENCE. 
when they first see them, and at that moment they 
must have struck against the atmosphere, 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 
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, 
measures exactly a square inch, 
and 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? 
To understand this you must give all your atten- 
tion, for it is important and at first not very easy to 
grasp. You must remember, in the first place, that 
the air is heavy because it is attracted to the earth, and 
in the second place, that since air is elastic all the atoms 
of it are pushing upward against this gravitation. And 
so, at any point in air, as for instance the place where 
FIG. 13. A square 
inch of paper, as 
shown in the lec- 
ture. 
