ICEBERGS IN NAVIGATION BARNES. 



721 



PETTERSSON S THEORY OF ICE MELTING. 



Dr. Otto Fettersson has for some time shown experimentally that 

 ice melting in salt water produces three currents (fig. 1). (1) When 

 the ice melts it cools the salt water, which sinks down by convection. 

 (2) A stream of warmer salt water moves in toward tlic ice, giving 

 rise to a horizontal current. (3) The melted ice consists of fresh 

 water, wliich does not mix with the salt water on account of the dif- 

 ference of density. Tliis fresh water rises around the ice and spreads 

 out over the surface. The ice becomes surrounded by a layer of 

 fresher water, which tends to remain on the surface. As the ice 



FtG. 1.— Ice melting in salt water. 



moves the fresh water moves witli it. Waves do not mix it with the 

 salt water, but leave it practically unaffected. Pettersson believes 

 that this circulation has an important influence on the cuiTents in the 

 sea. The lower density of a diluted layer prevents the normal ver- 

 tical circulation in the sea, and causes characteristic temperature 

 effects. 



Icebergs wliich have been left high and dry on tlie shore by the 

 tide sliow the action of the melting. Bergs whicli become top-lieavy 

 and turn over also bear evidence to the underwater current producing 

 the melting. The form of the ice shows a deep furrow running all 

 around where the melting process has proceeded, and this is often the 

 cause of the rolling over of a berg to find equilibrium in some other 



