386 NATURE STUDY AND LIFE 



the soil washes in the woods, in grass land, and where the 

 ground is bare. 



Next let us study how we can keep the soil at home 

 and make the water clear as crystal. Pour a tumbler of 

 muddy water into a filter and catch the water in a clean 

 glass as it comes through. In one of the bottles with the 

 bottom out make a filter of leaf mould, pack it well and 

 wash the dust out of it, if necessary, and then see how 

 clear muddy water may be made by passing through it. 

 Can we make it as clear as the water from the spring or 

 well ? Why not ? How deep is the filter through which 

 the spring water passes.? Do we need a very thick filter, 

 if it is fine enough ? 



Find a pond in the neighborhood with an inlet and outlet ; 

 a temporary one will serve the purpose if no permanent 

 ponds are available. Study the water that flows in and 

 compare it with that which flows out. Refer back to the 

 experiments of settling muddy water in the tumblers, and 

 call attention to the fact that the lighter particles remain 

 floating a long time and may even leave the pond by 

 the outlet. There are other ways of keeping the water 

 pure, which will be taken up when we study aquaria, but 

 these two, filtering and settling, are the chief methods 

 with which every plan for purification of surface waters 

 must begin. 



The water supply to a district is another topic closely 

 related to the foregoing. Does the water run off in 

 torrents after a rain and when the snows melt in the 

 spring ? Do the springs and wells go dry and the streams 

 fail in a long period of drought ? Are the springs and 

 streams generally lower than they used to be .'* If this 



