THE AERIAL OCEAN IN WHICH WE LIVE. 65 
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 upward, downward, 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, how- 
ever, 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.* I now drop it on this stone 
weight, and so heavily is it pressed down upon it 
by the atmosphere that I can lift the weight without its 
breaking away from it. 
Have you ever tried to pick limpets off a rock ? If 
so, you know how tight they cling. The limpet clings 
to the rock just in the same way as this leather does 
to the stone; the little animal exhausts the air inside 
* 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 ex- 
periment, not having taken these precautions, it did not succeed 
well, owing to air getting in through the hole. 
