336 ANTARCTIC CRUISE. 



many masters of vessels have met them, some six or seven hundred 

 miles from the barrier, from sixty to eighty days after this period, 

 which will give a near approximation to our results heretofore 

 stated. 



The season of 1839 and '40 was considered as an open one, from 

 the large masses of ice that were met with in a low latitude, by vessels 

 that arrived from Europe at Sydney : many of them were seen as far 

 north as latitude 42° S. 



The causes that prevail to detach and carry them north, are difficult 

 to assign. I have referred to the most probable ones that would 

 detach them from the parent mass in their formation. Our frequent 

 trials of currents, as has been stated, did not give us the assurance that, 

 any existed ; but there is little doubt in my mind that they do prevail. 

 I should not, however, look to a surface current as being the motive 

 power that carries these immense masses at the rate they move ; com- 

 paratively speaking, their great bulk is below the influence of any 

 surface current, and the rapid drift of these masses by winds is still 

 more improbable ; therefore I conceive we must look to an under 

 current as their great propeller. In one trial of the deep-sea thermo- 

 meter, we found the temperature beneath, four degrees warmer than 

 the surface. Off Cape Horn, the under temperature was found as cold 

 as among the ice itself; repeated experiments have shown the same to 

 occur in the Arctic regions. From this I would draw the conclusion 

 that changes are going on, and it appears to me to be very reasonable 

 to suppose, that at periods, currents to and from the poles should at 

 times exist ; it is true, we most generally find the latter to prevail, as 

 far as our knowledge of facts extends, but we have not sufficient infor- 

 mation yet to decide that there is not a reflow towards the pole ; the 

 very circumstance of the current setting from the higher latitudes, 

 w 7 ould seem a good argument that there must be some counter-current 

 to maintain the level of the waters. These masses, then, are most 

 probably carried away in the seasons when the polar streams are the 

 strongest, and are borne along by them at the velocity with which 

 they move : that these do not occur annually may be inferred from 

 the absence of ice-islands in the lower latitudes ; and that it is not 

 from the scarcity of them, those who shared the dangers of the 

 Antarctic cruise, will, I have little doubt, be ready to testify ; for, 

 although great numbers of them studded the ocean that year, yet the 

 narrative shows that vast numbers of them were left. 



The specific gravity of the ice varies very much, as might naturally 

 be expected ; for while some of it is porous and of a snowy texture, 



