"These little particles of water vapor, like the particles of steam, are so light that they rise in the air, and are at once sucked up or absorbed into its pores.
"We say that the water evaporates. We mean that it changes into vapor.""I have seen the water evaporate after a shower on a very hot day," said Will. "The vapor rises in a cloud from the wet pavements, and in a few minutes the stones are quite dry. On a cold day, too, the pavement dries up, but not so quickly as in the hot summer weather.""But you see," said Fred, "if it dries up at all, it proves that even in the cold weather the water evaporates. Let me explain it to you. It is the air which carries off the water, and it does this because it is porous and absorbent.
"Sometimes the air is so very dry that its pores contain little or no vapor. When this is the case the air becomes very thirsty. It will break up the water into tiny particles and suck them at once into its pores.
"The drier the air is, the quicker will be the evaporation. Clothes will dry on the line in cold weather as quickly as in hot, if the air is dry.
