ROLLERS. 
393 
Popular opinion lias ascribed the cause of the Pollers to dis- 
tant submarine volcanic action, but they occur with too much 
regularity to admit this reason, and I believe them to be due 
to oceanic currents, influenced by atmospheric pressure ; in fact, 
a return wave, caused by the meeting of the Antarctic waters 
with the great Equatorial current of the Gulf Stream, and in- 
fluenced by the North-east Trade winds. It is during the Poller 
months that the sun lias greatest power in the Tropical Southern 
Hemisphere, and therefore the greatest amount of evaporation takes 
place ; consequently the flow of cold water from the Antarctic regions 
towards the Equator is then most abundant and most rapid ; as this 
current gets well warmed by the time it approaches the Line, it is 
hotter than the water of the great Equatorial current flowing south 
round Cape Yerde, which it meets in latitude 4° South. These 
waters coming into violent collision, and not readily mixing because 
of difference in temperature, must result in a return current either 
northward or southward. This return takes place in the latter 
direction, after the Equatorial current has been forced to flow out 
on either side against the Brazilian and the African continental 
coasts.* The Equatorial current being at its maximum of strength at 
this period of the year is to a great extent due to the influence of the 
North-east Trade winds upon it, for it is their period of greatest force 
and most southern latitude. During the months of December to May 
the Equatorial limit of the North-east Trades is 5° to 7°N. la,., ex- 
guns away, for we had enough to do to save them. The same high seas has also broke the 
middle angle of the Trench in James Valley for a matter of one hundred and ten foot, and has 
damaged the angle where the round tower is of one gun insomuch as it was like to tumble 
(j 0W n!— These high seas sunk the punt and broke her loose, also the yaul, and nearly washed 
down the crane.” 
“ 5 April , 1715 — Wc think that a ship that arrives here about Christmas cannot pos- 
sibly be dispatched in less than a month, because of the very great surfes that usually happens 
about that time of the year. We are informed that the latter end of March and beginning of 
April is also a time when abundance of high seas do usually happen, and we are the more 
confirm’d in such an opinion because the Honhle : Companies long boat w ob brought eutt stone 
from Sandy Bay, w oh is at the Windermost part of the Island, has been laden these nine days, 
and is still loaden at a grapling in this road, hut the surf is so high and violent that we dare 
not attempt to unload her, neither with these seas is it possible that any boat with safety can 
come to tlie crane to be unlivered.” 
« 12 th April, 1715. This being the first day the Surfe abated the long boat was dis- 
patched again for Sandy Bay, and the Governor mencond it that it might appear w hat great 
seas we have sometimes, hut especially at this time of year, for now the great seas have held 
nineteen days, and the long boat was unloaden with much difficulty by smaller boats.” 
Rollers are also referred to as having occurred in March, 1717; December, 1733; Feb- 
ruary, 1720; and April, 1743.; 
