172 THE EEASON WHY. 



"Who hath measured the waters in the hollow of his hand, and meted out 

 heaven with the span, and comprehended the dust ot the earth in a measure 

 and weighed the mountains in scales, and the hills in a balance ?" ISAIAH XL. 



Because the water passes through beds of soda, lime, magnesia, 

 carbonic acid, oxides of iron, sulphate of iron, &c., &c., and takes up 

 in some slight degree the particles of those minerals, according to 

 the proportions in which they abound. 



768. W Jiy does iron rust rapidly when wetted ? 



Because the water contains a large proportion of oxygen, some 

 of which combines with the iron and forms an oxide of iron, which 

 is rust. 



769. Why does stagnant water become putrid ? 



Because the large amount of oxygen which it contains accelerates 

 the decomposition of dead animal and vegetable substances that 

 accumulate in it. 



770. Is there danger in drinking water on account of the 

 living animalcules which it contains ? 



No danger arises from the living creatures in water ; but 

 putrefactive matters may produce serious diseases. 



771. What is the best method of guarding against im- 

 purities ? 



By obtaining water from the purest sources, and by filtering 

 it before drinking, by which nearly all extraneous matters would be 

 separated from it. 



CHAPTER XXXVI. 



772. What is attraction ? 



Attraction is the tendency of bodies to draw near to each other. 

 It is called attraction, from two Latin words signifying drawing 

 towards. 



773. Sow many kinds of attraction are there ? 

 There are five principal kinds of attraction : 



1. The attraction of gravitation. 



2. The attraction of cohesion. 



8. The attraction of chemical affinity. 



