242 THE SEAS 



by the temperature changes occurring in its interior after 

 the explosion, the cracking of the berg into pieces sounding 

 like a series of gun reports. 



Since the tragic sinking of the Titanic by an iceberg, 

 an Ice Patrol Service is on constant duty to give warning 

 to passing ships of the presence of the bergs and to study 

 their drift and movements. 



Curiously enough one of the first signs of an approaching 

 iceberg is a rise in the temperature of the water. The 

 surrounding sea water on bathing the ice becomes cooled 

 and hence heavier, and sinks, and more warm water flows 

 in to take its place. But the fresh water from the melting 

 of the exposed part of the berg pours down off its sides 

 into the sea. Owing to its freshness it is considerably 

 lighter than the sea water and floats at the surface. 

 Similarly water from the ice melting below the sea surface 

 rises. Fresh water heats up more readily than salt water, 

 so that this lake of fresh water which surrounds the iceberg 

 on all sides gains more heat from the sun than the sea water 

 (Fig. 47). 



