96 Temperature Sections Surveyed. 



exquisite azure-blue light which filled the numerous caves 

 worn by the waves in their flanks. On the day when the 

 ship stopped in lat. 66° \o' S., long. ']%" 22' E. — a distance 

 of 1400 nautical miles from the South Pole — more than 

 seventy of these floating islands of ice could be counted 

 from her deck, one of them over five miles long, and rising 

 from 150 to 200 feet above the sea. 



The melting of these ice-masses produces a quantity of water, 

 which, being fresher, is of less specific gravity than the salt 

 water of the surrounding sea, and therefore floats in the immediate 

 vicinity of the ice on the surface of the latter. But as the fresher 

 water derived from the icebergs mixes by degrees with the sur- 

 rounding salt water, the mixture being of lower temperature is 

 rendered heavier, and sinks below the surface, forming an inter- 

 mediate stratum or wedge, as shown in Plates 12 and 13. 



Owing to her supplies of coal running short, H.M.S. 

 " Challenger " was prevented from establishing as many stations 

 between the Ice-barrier and Australia as might have been 

 desirable, but suflicient observations were secured to confirm 

 the existence and to ascertain the proportions of the great 

 current which, under the name of the South Australian Current, 

 was already known to flow in an easterly direction at some 

 distance from the south coast of the Australian continent. 



The temperature of the water, which at Station 157 was 

 2°. 9 C. at the surface, 2°. 6 C. at 60 fathoms, o°.6 C. at 70 

 fathoms, and o°.3 C. at 80 fathoms — thus betraying the presence 

 of an overflowing warmer current — and — o°.6 C. at the bottom 

 in 1950 fathoms, had risen at Station 158 to 7°. 2 C. at the 

 surface, 5° C. at 200 fathoms, 2° C. at 700 fathoms, 1° C. at 1500 

 fathoms, and o.^, C. at the bottom in 1800 fathoms. At Station 

 159 there appeared evident signs of the presence of a warm 

 under-current, for the temperature of the water, which between 

 the surface and 100 fathoms had fallen from 10°. 8 C. to 



