150 
THE PHYSICAL GEOGRAPHY OF THE SEA. 
CHAPTER VIIL 
THE SALTS OF THE SEA. 
What the Salt in the Sea Water has to do with the Currents in the Ocean, ^ 289. — 
Reasons for supposing the Sea to have its system of Circulation, 290. — Arguments 
furnished by Coral Islands, 293. — What would be the Effect of no system of Cir- 
culation for Sea Water 1 295. — Its Components, 297. — The principal Agents from 
which Dynamical Force in the Sea is derived, 300. — Illustration, 302. — Sea and 
Fresh Water have diflerent Laws of Expansion, 308. — The Gulf Stream' could not 
exist in a Sea of fresh Water, 309. — The effect of Evaporation in producing Cur- 
rents, 310. — How the Polar Sea is supplied with Salt, 323. — The Influence of this 
under Current upon open Water in the Frozen Ocean, 326. — Sea Shells : The 
Influence exerted by them upon Currents, 330. — Order among them, 335. — They 
assist in regulating Climates, 336. — How Sea Shells and Salts act as Compensa- 
tions in the Machinery by which Oceanic Circulation is conducted, 339. — W^hence 
come the Salts of the Sea ■? 344. 
288. In order to comprehend aright the currents of the sea, and 
to study with advantage its physical adaptations, it is necessary to 
Understand the effects produced by the salts of the sea upon the 
equilibrium of its waters ; for wherever equilibrium be destroyed, 
whether in the air or water 276), it is restored by motion, and 
motion among fluid particles gives rise to currents, w^hich, in turn, 
constitute circulation/ 
This chapter is therefore added as a sort of supplement, which 
will assist us in elucidating what has been advanced concerning 
the currents of the sea. 
289. The question is often asked, " Why is the sea salt ?" I 
think it can be shown that the circulation of the ocean depends, 
in a great measure, upon the salts of sea water ; certainly its in- 
fluences upon climate are greatly extended by reason of its salt- 
ness. 
As a general rule, the sea is nearly of a uniform degree of salt- 
ness, and the constituents of sea water are as constant in their 
' proportions as are the components of the atmosphere. It is true 
that we sometimes come across arms of the sea, or places in the 
ocean, where we find the water more salt or less salt than sea 
