TEMPERATURE OF THE SEA 483 



Temperature of the Sea. — The heating effect of 

 the sun on ocean water is not perceptible below a depth 

 of about one hundred feet, and obviously is most marked 

 in tropical regions. Owing to the rotation of the earth 

 and the restraining influence of the continental land 

 masses this heated water is made to travel in great 

 circles in both the northern and southern hemispheres. 

 In the north Atlantic this current is named the Gulf 

 Stream, while the corresponding one in the north Pacific 

 is the Japan Current. The deeper waters of the ocean, 

 since these are unaffected by the sun, probably remain at 

 about the same temperature from year to year; and, it 

 may be added, the temperature in deep water is close to 

 freezing at the bottom and gradually rises as the surface 

 is approached. 



Effect of Ocean Currents. — It may perhaps be 

 unnecessary to call attention to the fact that these oceanic 

 currents are of the highest importance in the distribution 

 of life in the sea. Not only do they carry the floating 

 animals and plants for thousands of miles and thus 

 establish many species in homes they would otherwise 

 never occupy, but also, to a large extent, they govern the 

 migration of fishes and whales that prey upon this food 

 and are thus of great importance to the fishing industry. 



Pressure. — The air presses upon our bodies and other 

 objects with a weight of about 15 pounds to the square 

 inch at sea level. In the sea the pressure is doubled at 

 a depth of 35 feet, and continues to increase at practically 

 the same rate to the greatest depths. Accordingly the 

 body of a man, if sunk to the bottom of the deep off the 

 Philippines, would support the enormous weight of 

 approximately 31,000,000 lbs. Since animals are known 

 to live at a depth of at least three miles the question 

 naturally suggested is, how is this possible when the 

 pressure amounts to considerably more than 6,000 lbs. 

 per square inch. It is chiefly because the body is largely 

 composed of water, and water is practically incompres- 



