CLOUDS. FOGS. MIST. RAIN. 37 



densed, they give out the heat which had sustained them 

 in the form of gas. 



And, in like manner, when Water Freezes, it gives out 

 the Heat which it had taken in, while turning from ice 

 into water. We thus see why it happens that, to protect 

 vegetables, in a cellar, against freezing, we have only to 

 place tubs of water there, the warmer the better. The 

 temperature of the cellar will not fall below the freezing 

 point, till the water has been converted into ice. 



111. The atmosphere always contains moisture ; that 

 is, water in the state of vapor, which the heat of the sun 

 has drawn up from the surface of the earth and sea, and 

 which floats, invisible, in the air. The warmer the air is 

 the more water it can contain. When the air cools, the 

 invisible vapor which it contained becomes visible in little 

 hollow globules or vesicles, like minute soap bubbles, and 

 forms clouds, fogs and mists. 



112. The difference between clouds and fogs or mists 

 is chiefly their situation. Clouds are at a distance or 

 high up in the air ; Togs are clouds near the earth ; and 

 if the fog be thick enough to wet us considerably, without 

 drops, we call it Mist. When a person, looking at a dis 

 tant mountain, sees it capped with a cloud, another per 

 son, standing on the top of the mountain, finds himself 

 surrounded by fog or mist. 



113. Rain. The air itself may be capable of dissolving 

 water, but the quantity which the air can hold depends 

 upon its warmth. 



Wind which has long been blowing over the sea becomes 

 completely saturated with moisture in the state of vapor. 

 If it now blow upon low land warmer than itself, the air 

 becomes warmer and retains all its moisture ; if upon 

 land colder and gradually or rapidly higher, it is cooled 



