All of these men returned valuable observations with the hydrometer, though Captain Rodgers afforded the most extended series.
Those navigators who used the hydrometer enlarged the bounds of knowledge and fields of research and led to the discovery of new relations of the sea.
The object which the Brussels Organization had in view when the specific gravity column was introduced into the sea-journal was that hydrographers might find in it data for computing the dynamical force which the sea derives for its currents from the difference in the specific gravity of its waters in different climes.
The observations made with it by Captain Rodgers, on board the Vincennes – the first United States warship to circumnavigate the globe – showed that the specific gravity of sea water varies but little in the trade-wind regions, notwithstanding the change of temperature.
But, though the sea at the equatorial borders of the trade-wind belt is some 20° or 25° warmer than it is on the polar edge, the specific gravity of its waters at the two places in the Atlantic differs but little.