Bibliography. 165 
would lead to the belief, that great changes must take place in the higher lati- 
tudes, or the prevalence of some cause to detach the ice-islands from the barrier 
in such great quantities as to cover almost the entire section of the ocean, south 
of the latitude 50° S. Taking the early part of the (southern) spring, as the time 
of separation, we are enabled to make some estimate of the velocity with which 
they move: 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° 8S. 
“ 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 pa- 
rent 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 ; 
comparatively 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 thermometer, 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 oceur 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 information yet to decide that there is not a reflow 
towards the pole; the very circumstance of the current setting from the higher 
latitudes, would seem a good argument that there must be some counter-current 
to maintain the level of the waters. ‘These masses, then, are most probably car- 
ried 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 
Antaretie 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 ex- 
pected ; for while some of it is porous and of a snowy texture, other: islands are 
in great part composed of a compact blue flinty ice. This difference is occasioned 
by the latter becoming saturated with water, which afterwards freezes. 
‘*On the ice there was usually a covering of about two feet of snow, which in 
places had upon it a crust of ice not strong enough to bear the weight of a man. 
Those ice-islands, which after having been once seen, were again passed through 
immediately afier a gale, were observed to be changed in appearance; but though 
for forty-eight hours a severe storm had been experienced, they had not undergone 
so great a transformation as not to be recognized. ‘They also appeared to have 
shifted their position with regard to one another, their former bias and trendings 
being broken up. 
‘‘ During our stay on the icy coast, I saw nothing of what is termed pack-ice— 
that is, pieces forced one upon the other by the action of the sea or currents. 
