Contrasting Qualities of Air and Water 25 



of 79 per cent nitrogen, 21 per cent oxygen, 0.03 per cent carbon 

 dioxide, and several other gases in much smaller quantities. These 

 gases are not chemically combined, but exist as a simple physical 

 mixture. Water, by contrast, consists primarily of a single compound, 

 H:,0. There is nothing especially unusual about the physical and 

 chemical properties of air and the gases of which it is composed. 



U. S. Forest Service 



Fig. 2.2. Pond formed by beaver dam (left foreground), showing beaver house 

 (right center) and trees felled and stripped by the beavers. Cochetopa National 



Forest, Colorado. 



Water, on the other hand, is a unique substance from the ecological 

 viewpoint. H. B. Bigelow, formerly director of the Woods Hole 

 Oceanographic Institution, when lecturing on oceanic biology once 

 stated: "The most important fact about the ocean is that it is full of 

 water!" 



The unusual qualities of water are discussed in detail by Henderson 

 (1924) in his classic book, Tlie Fitness of the Environment. Suffice 

 it here to mention a few of the attributes of water that have a special 

 ecological importance. In the first place water is the most abundant 

 substance of the earth's surface, covering more than 70 per cent of the 

 area of the globe. Because the oceans are about 2% times more 

 extensive than the land, and because they are habitable throughout 

 their depth, the sea provides more than 300 times the living space. 

 Water has a higher specific heat, latent heat of fusion, and latent 



