250 A NATURALIST OX THE " CHALLENGER." 



the overhanging edges at that level looked blue. The upper 

 masses were quite opaque. 



I went in a boat to collect discoloured ice. The discoloura- 

 tion appears far less marked when the ice is seen at close 

 quarters. It becomes almost invisible when the porous snow- 

 ice drains dry. When however a small piece of the ice is 

 seen floating nearly submerged, it looks almost of a chocolate 

 brown colour. 



Mr. Buchanan made experiments on the melting point, and 

 amount of salt contained in salt-water ice. He came to the con- 

 clusion from analyses of successive meltings and the varying of 

 the melting point, that in salt-water ice " the salt is not contained 

 in the form of mechanically enclosed brine only, but exists in 

 the solid form, either as a single crystalline substance, or as a 

 mixture of ice and salt crystals." 



He thinks that by fractional melting, salt water ice might be 

 made to yield water fit to drink, although when a lump is 

 melted as a whole, the resulting water is undrinkable.* 



We crossed the Antarctic Circle on February 16th, passing 

 about six miles to the south of it. There was open water ahead, 

 but the " Challenger " was not strengthened for ice work, and we 

 were not ordered to proceed further south, so we turned back. 

 There seemed to be a deep opening in the pack here, nearly due 

 south of Heard Island. We subsequently passed within six miles 

 of what is marked on maps as Wilkes' Termination Land, and 

 found that this did not exist. Wilkes no doubt was deceived by 

 the land-like appearance of distant icebergs. It is to be noted 

 that he merely says that he saw appearance of land here, sixty 

 miles distant, but high and mountainous. Others have named 

 it for him and placed it on the charts. 



On two occasions, whilst amongst the southern ice, our ship 

 was in some little danger, having to ride through heavy gales of 

 wind amongst numerous icebergs in thick weather. 



On the morning of February 24th there was a fresh breeze, 

 in which we sounded in 1,300 fathoms, and attempted to dredge, 



* J. V. Buchanan, M.A., "Observations on Sea- Water Tee," Proc. H. 

 Soc., No. 170, 1870, p. (509. 



