WYVILLE THOMSON 55 



area which stretches S.W. from the line of demarcation the 

 temperature is 47° F. at 250 fathoms and 42° at the bottom 

 in 600 fathoms. The warm area was found to have 216 

 species, while the cold had 217, and of these only 48 species 

 were common to both. 



Sir Wyville Thomson (see Nature, Sept. 2, 1880), as a 

 result of his consideration of the " Challenger " temperatures, 

 came to the conclusion that the cold and warm areas of the 

 Faroe Channel must be separated by a very considerable 

 submarine ridge rising to within 200 or 300 fathoms of the 

 surface. He therefore addressed a letter in June, 1880, to the 

 Hydrographer of the Admiralty, pointing out these facts, and 

 asking for the use of a surveying vessel for a few weeks for 

 the purpose of sounding the Faroe Channel with a view of 

 testing his prediction. That was the origin of the " Knight 

 Errant " expedition conducted by Captain Tizard and 

 Dr. John Murray, under the general direction of Sir Wyville 

 Thomson, who remained at Stornoway in the Outer Hebrides 

 during the four traverses of the region in question. The 

 results ^ completely justified Sir Wyville Thomson's predic- 

 tion, and showed that a ridge rising to within 300 fathoms of 

 the surface runs from the N.W. of Scotland by the Island of 

 Rona to the southern end of the Faroe fishing banks. 



This was followed by a further expedition in H.M.S. 

 " Triton" in the summer of 1882, again under Murray and 

 Tizard, which was very fruitful of zoological results. The 

 discovery of two very different assemblages of animals 

 living on the two sides of the Wyville Thomson ridge — Arctic 

 forms to the north and Atlantic forms to the south — gives 

 us a notable example of the effect of the environment on the 

 distribution of marine forms of life. 



Sir Wyville Thomson, however, did not live to see the 



" Triton " expedition and the full results of the exploration of 



the submarine ridge which so appropriately bears his name. 



His health had been failing for several years. In June, 1879, 



1 Published in the Proc. Roy. Soc. Edin. for 1882 (Vol. XI). 



