small drops will grow larger Ijy more vapor turning into water, and 

 finally they become large enough to fall rapidly as rain. Y»u may 

 somatimes, but not often, find that rain falls before any clouds are 

 formed. This is due to a very cold wind suddenly blowing in and 

 chilling the air a short distance above us, so that the vapor quickly 

 turns into large drops, which fall as rain. You will find it interesting 

 to note the direction from which the wind that brings rain usually 

 comes. If you keep a list in your notebook you may soon become 

 quite an authority on the weather. 



After writing the last two sentences I remembered that it is some- 

 times very difficult to tell from wlmt direction the wind really does 

 come, and when the wind is very light you will probably find this dif- 

 fi»ulty. You may then try the method that sailors sometimes use 

 when they wisli to find from what direction a very faint wind is 

 springing up. Wet one of your fingers and hold it up. "Wait until it 

 begins to dry, and you ^A-ill feel one side of it much colder than the 

 rest. That is the side of it on which the wind blows. You can detect 

 the very slightest wind in this way. If you open the outside door 

 of a warm room a couple of inches and hold a wet finger at the bottom 

 of the opening, then at the top and then at points near the middle, 

 you will be able to learn something very interesting about how air 

 circulates. 



But this experiment can teach us more than the direction of the 

 wind. AVe learn from it that when -n-ater dries up from any surface 

 it leaves the surface colder; that is, the vapor takes heat away with 

 it. In fact, the heat is needed in all cases to turn the water into 

 vapor. Try wetting one side of your face and then standing so as to 

 face the wind, and then you will perhaps be able to explain why a 

 little little wind is so very agreeable on a warm day. Is it because the 

 wind itself is cool? There are some hot summer days when the wind 

 does not seem to cool us at all. If you notice you will find these are 

 daj's on which the air itself seems moist; some people describe the 

 weather as "muggy." Can you explain wliy hot weather is so much 

 more oppressive when the air is moist? 



While speaking of the cold produced by water turning into vapor, 

 let me suggest another experiment: Some hot summer day take two 

 bottles of luke-warm i,vater; wrap a \\-et towel around one and put 

 them out in the shade where the wind will blow on them, and after 

 the towel has nearly dried see if there is any difference between the 

 two bottles as regards the taste of the water. You will then know 

 how to get cool water on a hot day. If you find that on some days 

 you cannot get this plan to ^\ork well, you should see if you can ex- 

 plain the cause. 



