122 



NATUKE FOB ITS OWN SAKE 



Depth of 

 the undu- 

 lation. 



Local hues. 



slowly. A chip rises and pitches forward on a 

 crest, but it is drawn back almost an equal dis- 

 tance into the succeeding hollow. Eventually 

 it is carried many miles, to be tossed perhaps 

 upon some island shore ; but it makes a very 

 slow passage. 



The undulation is generally supposed to be 

 only a surface affair a disturbance like the 

 ringed waves that ride shoreward from a stone 

 cast in a pond. And so it may be ; but the depth 

 at which the movement is felt is often very great. 

 In the bays and harbors along shore a wave four 

 feet in height can be seen swaying and tossing 

 the sea- weed many feet below the surface, and 

 in the Mediterranean, where the water is very 

 clear, the bottom of a swell has been seen rush- 

 ing through rock passages twenty-five fathoms 

 down. There is little doubt that the heaviest 

 waves can be felt a hundred fathoms below the 

 surface. 



The local color of sea water is determined by 

 its density, its depth, the ground underneath 

 it, or foreign matter held in it. Salt water is 

 denser and generally bluer than fresh water, 

 and the regions of intense salinity are generally 

 the deepest hued of all. The Mediterranean, 

 the Red Sea, the Caribbean are at times violet- 



