A DROP OF WATER. 77 
upon our earth, they carry off invisible water-vapour. 
They dart down through the top layers of the water, 
and shake the water-particles forcibly apart ; and 
in this case the drops fly asunder more easily and 
before they are so hot, because they are not kept 
down by a great weight of water above, as in the 
kettle, but find plenty of room to spread themselves 
out in the gaps between the air-atoms of the atmo- 
sphere. 
Can you imagine these water-particles, just above 
any pond or lake, rising up and getting entangled 
among the air-atoms ? They are very light, much 
lighter than the atmosphere ; and so, when a great 
many of them are spread about in the air which lies 
just over the pond, they make it much lighter than 
the layer of air above, and so help it to rise, while 
the heavier layer of air comes down ready to take 
up more vapour. 
In this way the sun-waves and the air carry off 
water every day, and all day long, from the top of 
lakes, rivers, pools, springs, and seas, and even from 
the surface of ice and snow. Without any fuss or 
noise or sign of any kind, the water of our earth 
is being drawn up invisibly into the sky. 
It has been calculated that in the Indian Ocean 
three-quarters of an inch of water is carried off from 
the surface of the sea in one day and night ; so that 
as much as 22 feet, or a depth of water about twice 
the height of an ordinary room, is silently and in- 
visibly lifted up from the whole surface of the ocean 
in one year. It is true this is one of the hottest parts 
of the earth, where the sun-waves are most active ; 
