NATURE FOR 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 wayes that ride shoreward from a stone 
castinapond. And soitmay 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- 
