The principle of constant ratios between the salts in ocean water unaffected by land drainage was laid down by Forchhammer in 1864, and firmly established by Dittmar (1884) . Dittmar's examination of 77 samples, collected from all the oceans of the world by H .M.S. Challenger in 1873-76, was so comprehensive, and his results so consistent, that some of his values are used to this day.