154 



FOUNDERS OF OCEANOGRAPHY 



under special conditions, vertical currents may be formed, 

 causing deeper layers of colder water, with their contained 

 organisms, to rise to the surface. 



Fia. 7. — Diagram showing effect of Wind on distribution of 

 Temperatures in Loch Ness. {After Murray.) 



Salinity. 

 As all the water running off the land into the sea dissolves 

 and carries with it materials from the rocks and the soil, it 

 is probable that the ocean contains samples, even if only 

 minute traces, of every mineral substance found on earth. 

 Over thirty of the known elements have been found in sea- 

 water, and more than a dozen of these are in such quantity 



m'nd 



Fig. 8. — Diagram showing effect of Off-and On-shore Winds at Sea. 



as to be of real importance. These contained " salts " of 

 sea-water amount on the average to thirty-five parts in 

 a thousand parts of water, and are chiefly chlorides and 

 sulphates of sodium, magnesium, potassium and calcium. 

 Chloride of sodium (common salt) makes up more than three- 



