174 FIRESIDE SCIENCE. 



even the hottest air holds a vast amount of water, 

 it only needs to be brought in contact with refrig- 

 erating substances to produce a copious precipita- 

 tion of water. All of us have observed large drops 

 of water form upon and trickle down the sides of 

 our ice-pitchers in the hottest days of summer. 

 This water is condensed from the warm and ap- 

 parently dry air, which comes in contact with the 

 ice-cold surface of the vessel. This will illustrate 

 the way in which the soil is moistened through the 

 agency of drain pipes. The earth, at a distance 

 of one foot from the surface, is several degrees 

 cooler than the air above, and consequently when 

 it passes in through the open ducts, it parts with its 

 hidden moisture, and the vapor is diffused through 

 the soil. Water readily travels through burnt clay, 

 when unglazed. This we know from the fact that 

 if we build a water cistern of bricks, and omit to 

 cover the inside with hydraulic cement, the water 

 will run out as fast as it runs in. The best possible 

 water filter that can be devised is constructed by 

 building inside of a rain water cistern, lined with 

 cement, a brick chamber, which will rapidly fill 

 with water by passing through the bricks. In its 

 passage it is deprived of all impurities and becomes 

 pure and excellent suitable for all household pur- 

 poses. A pump passing into the chamber will 

 bring this pure water to the desired point above, 



