CORAL REEFS OF TORRES STRAITS 



223 



As we have seen, the " lagoon " of the reef flat on the southeast side 

 of Maer Island is shallow, being only about 18 inches deep at the lowest 

 tide, although covered by about 8 feet of water at high tide. When the 

 low tide falls at the hottest part of the day, at about 3 o'clock in the 

 afternoon, the water of the reef flat is several degrees warmer than the 

 air, but in the early morning before sunrise, the water is always colder 

 than the air. This shows that the lagoon water derives most of its heat 

 during the day from direct solar radiation, and at night the surface of 

 the water radiates heat into outer space and thus becomes colder than 

 the air. It has been commonly supposed that the temperature range of 

 ocean water is less than that of the air, but this is evidently not the case 

 in shallow lagoons in the tropics where the range in air temperature is 

 slight. Indeed, during five weeks in September and October at the 

 Murray Islands, the difference in air temperature between the hottest 

 day and coolest night was only 10° F., the hottest being 86° and the 

 coolest 76° ; but during the same time the water over the southeast reef- 



mam 



m& 



Natives of Kuranda, Queensland, standing in front of their house. Australian 



aborigines. 



