TEMPERATURE OF OCEAN WATERS 279 



high," it rarely happens that the height from trough to 

 crest is over 50 ft. The length of these great ocean waves, 

 or the distance from crest to crest or from trough to trough 

 varies from 300 to 1500 ft. or more. The velocity is 

 sometimes as great as 60 miles per hour, but usually not 

 more than half of this. The movement of the waves stirs 

 up the water and enables it to absorb the air which is so 

 necessary for the existence of water animals. 



Earthquakes occurring under the sea sometimes gen- 

 erate great waves which sweep in over the land destroying 

 coast towns and shipping. These waves sometimes rise 

 to a height of even a hundred feet above sea level. Ships 

 have been carried by them a long distance inland and left 

 high and dry. These waves, wrongly called tidal waves, 

 have no connection with the wind. 



132. Temperature of Ocean Waters. Experiment 125. Fill 



a flask of about 500 cc. with water. Press into the mouth of the 

 flask a cork through which a glass tube about 30 cm. long extends. 

 The tube should be open at both ends and should not extend into the 

 flask below the bottom of the cork. When the cork is pressed in, the 

 water will be forced up into the tube for several centimeters. See 

 that the cork is tight and that there are no bubbles of air in the flask 

 or tube. 



Now place the flask for fifteen or twenty minutes in a mixture of 

 ice and water and carefully mark with a rubber band the point at 

 which the water in the tube comes to rest. Take the flask out of the 

 freezing mixture and notice immediately whether the water in the 

 tube rises or falls. Continue for five or ten minutes to notice 

 the action of the water in the tube. The volume of the water is not 

 the least when it is at the temperature of melting ice, 32 F., but 

 when it is a little above this temperature. 



Unlike fresh water, which is densest at a little above 

 freezing, sea water continues to decrease in volume and 

 grows denser as it is cooled, until it reaches its freezing 

 point at 28 F. Hence the cold water near the poles 



