410 THE ANTARCTIC MANUAL. 
Much inquiry and a strong desire has been evinced by geologists to 
ascertain the extent to which these ice-islands travel, the boulders and 
masses of earth they transport, and the direction they take. 
From my own observations and the information I have collected, 
there appears a great difference in the movements of these vast masses ; 
in some years great numbers of them have floated north from the 
Antarctic Circle, and even at times obstructed the navigation about the 
Capes. The year 1832 was remarkable in this respect ; many vessels 
bound round Cape Horn, from the Pacific, were obliged tu put back to 
Chili, in consequence of the dangers arising from ice; while during 
the preceding and following years little or none was seen; this would 
lead to the belief that great changes must take place in the higher 
latitudes, 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 600 or 700 miles from the barrier, from 
sixty to eighty days after this period, which will give a near approxi- 
mation to our results heretofore stated. 
The season of 1839 and 1840 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; 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 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 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 
