20 C. HEDLEy. 



incomplete sea surface temperatures range from 44*1° to 



58'9V 



The temperature of the water both in Sydney Harbour 

 and along the coast is altogether governed by the Noto- 

 nectian Current, the Gulf Stream of Australia. 2 In mid- 

 winter this is blown off shore and the temperature normal 

 to the latitude then prevails. But in midsummer the Noto- 

 nectian running at its highest volume, speed and tempera- 

 ture, hugs the land and overflows the harbour water. Thus 

 a warmth is attained, independent of the locality, which 

 may temporarily establish tropical conditions. If conti- 

 nental land were to arise once more between New Zealand 

 and New Guinea, then this current would be shut off from 

 the Australian coast, and both our climate and our fauna 

 would change at once. 



The critical temperature, that which determines life or 

 death for plants and animals, is likely here to be the mini- 

 mum. A low spring tide of a winter's night must be the 

 trial for existence of all intertidal life. 



SALINITY. 



Scarcely any observations have been made on the salinity 

 of the sea water in the neighbourhood of Sydney. From 

 the irregularity of the rainfall, the absence of large streams 

 flowing into the harbour, and the clearness of the water to 

 the eye, it is apparent that the salinity is unusually high 

 for a coast station. At the upper ends of the inlets the 

 water is of course more fresh and muddy than at the 

 entrance. 



Mr. T. W. Fowler has published some observations on the 

 density of sea water off the coast of New South Wales. 3 



1 Journ. Mar. Biol. Assoc, ii, 1892, p. 276. 



2 Hedley, Proc. Linn. Soc. N. S. Wales, xxxv, 1910, p. 9. 



3 Fowler, Eep. Aust. Assoc. Adv. Science, 1898, p. 695. 



