Certain ships of the

United States Navy The United States Navy (USN) is the maritime service branch of the United States Armed Forces and one of the eight uniformed services of the United States. It is the largest and most powerful navy in the world, with the estimated tonnage ...

adopted the use of the

hydrometer A hydrometer or lactometer is an instrument used for measuring density or relative density of liquids based on the concept of buoyancy. They are typically calibrated and graduated with one or more scales such as specific gravity. A hydrometer ...

in the 1850s. Readings taken of the

density Density (volumetric mass density or specific mass) is the substance's mass per unit of volume. The symbol most often used for density is ''ρ'' (the lower case Greek letter rho), although the Latin letter ''D'' can also be used. Mathematical ...

seawater Seawater, or salt water, is water from a sea or ocean. On average, seawater in the world's oceans has a salinity of about 3.5% (35 g/L, 35 ppt, 600 mM). This means that every kilogram (roughly one liter by volume) of seawater has appro ...

contributed to research into the dynamics of

ocean current An ocean current is a continuous, directed movement of sea water generated by a number of forces acting upon the water, including wind, the Coriolis effect, breaking waves, cabbeling, and temperature and salinity differences. Depth contours, s ...

Adoption

The first International Maritime Conference held at Brussels in 1853 (aka "Brussels Conference") for devising a uniform system of meteorological observations at seaMaury, Matthew Fontaine, USN, 1853
Brussels - First International Maritime Conference Held For Devising An Uniform System Of Meteorological Observations At Sea
WikiSource recommended the systematic use of the

. Captain John Rodgers, Lieutenant Porter, and Dr. William Samuel Waithman Ruschenberger, all of the

did this as did Dr. Raymond, in the American steamer ''Golden Age'', and Captain

Henry Toynbee Henry Toynbee FRAS FRGS (22 October 1819 – 29 March 1909) was an merchant sailor and an early meteorologist, whose career was dedicated to passing on his expertise. He introduced local weather-forecasting to the British Isles. Personal life Hen ...

, (F.R.A.S., F.R.A.G.S) of the English East Indiaman ''Gloriana''. All of these men returned valuable observations with the

, 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 Relative density, or specific gravity, is the ratio of the density (mass of a unit volume) of a substance to the density of a given reference material. Specific gravity for liquids is nearly always measured with respect to water (molecule), wa ...

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 Brussels Conference agreed that a given difference as to specific gravity between the water in one part of the sea and the water in another would give rise to certain currents, and that the set and strength of these currents would be the same, whether such difference of specific gravity arose from difference of temperature or difference of saltiness, or both.

Findings

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. The temperature was a little greater in the southeast trade-wind region of the Pacific; less in the Atlantic. 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. Though the temperature of the water was noted, his observations on its specific gravity have not been corrected for temperature.

Sources

Matthew Fontaine Maury Matthew Fontaine Maury (January 14, 1806February 1, 1873) was an American oceanographer and naval officer, serving the United States and then joining the Confederacy during the American Civil War. He was nicknamed "Pathfinder of the Seas" and i ...

, ''Physical Geography of the Sea'', sect.433-34
Captain "Henry" Toynbee
New South Wales marine records Oceanography {{US-navy-stub