57. What is the difference between hydrography and ocean- 

 ography? 



To explain the difference between hydrography and oceanography, 

 the ocean can be compared to a bucket of water; then hydrography is 

 the study of the bucket and oceanography is the study of the water. 



Hydrographers are primarily concerned with the problems of naviga- 

 tion. They chart coast lines and bottom topography. A hydrographic 

 survey usually includes measurement of magnetic declination and dip, 

 tides, currents, and meteorological elements. 



Oceanography is concerned with the application of all physical and 

 natural sciences to the sea. It includes the disciplines of physics, chem- 

 istry, geography, geology, biology, and meteorology. 



Physical oceanography is primarily concerned with energy transmis- 

 sion through ocean water, specifically with such items as wave forma- 

 tion and propagation, currents, tides, energy exchange between ocean 

 and atmosphere, and penetration of light and sound. 



Chemical oceanography is a study of the chemical properties of sea 

 water, of the cause and effect of variation of these properties with time 

 and from place to place, and of the means of measuring these proper- 

 ties. 



Biological oceanography is the study of the interrelationship of 

 marine life with its oceanic environment. The study includes the dis- 

 tribution, life cycles, and population fluctuations of marine organisms. 



Geological oceanography deals with the floor and shore of the oceans 

 and embraces such subjects as submarine topography, geological struc- 

 ture, erosion, and sedimentation. 



The interrelationship of specialties is one of the main characteristics 

 of oceanography. Oceanographic and hydrographic surveying may be 

 combined on the same ship. 



Many times the words "oceanography" and "hydrography" are used 

 interchangeably. 



Bowditch, Nathaniel 



American Practical Navigator, U. S. Naval Oceanographic Office, 

 1958. 



67 



