THE AERIAL OCEAN IN WHICH WE LIVE. 6l 
To understand this you must give all your attention 
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 upwards against this gravitation. And 
so, at any point in air, as for instance the place where 
the paper now is as I hold it up, I feel no pressure, 
because exactly as much as gravitation is pulling the 
air down, so much elasticity is resisting and pushing it 
up. So the pressure is equal upwards, downwards, 
and on all sides, and I can move the paper with equal 
ease any way. 
Even if I lay the paper on the table this is still 
true, because there is always some air under it. 
If, however, I could get the air quite away from one 
side of the paper, then the pressure on the other 
side would show itself. I can do this by simply 
wetting the paper and letting it fall on the table, and 
the water will prevent any air from getting under it 
Now see ! if I try to lift it by the thread in the 
middle, I have great difficulty, because the whole 
15 pounds' weight of the atmosphere is pressing it 
down. A still better way of making the experiment 
is with a piece of leather, such as the boys often 
amuse themselves with in the streets. This piece of 
leather has been well soaked. I drop it on the floor, 
and see ! it requires all my strength to pull it up.* 
* In fastening the string to the leather the hole must be very small 
and the knot as flat as possible, and it is even well to put a small piece 
of kid under the knot When I first made this experiment, not having 
taken these precautions, it did not succeed well, owing to air getting in 
through the hole. 
