140 
THE PHYSICAL GEOGRAPHY OF THE SEA. 
run with great force. On a voyage from the Society to the Sand- 
wich Islands, I encountered one running at the rate of ninety-six 
miles a, day. 
And what else should we expect in this ocean but a system of 
currents and counter-currents apparently the most uncertain and 
complicated ? The Pacific Ocean and the Indian Ocean may, in 
the view we are about to take, be considered as one sheet of wa- 
ter. This sheet of water covers an area quite equal in extent to 
one half of that embraced by the whole surface of the earth ; and, 
according to Professor Alexander Keith Johnston, who so states 
it in the new edition of his splendid Physical Atlas, the total an- 
nual fall of rain on the earth's surface is one hundred and eighty- 
six thousand, two hundred and forty cubic imperial miles. Not 
less than three fourths of the vapor which makes this rain comes 
from this waste of waters ; but supposing that only half of this 
quantity, i. e., ninety-three thousand, one hundred and twenty 
cubic miles of rain falls upon this sea, and that that much, at 
least, is taken up from it again as vapor, this would give two 
hundred and fifty-five cubic miles as the quantity of water which 
is daily lifted up and poured back again into this expanse. It is 
taken up at; one place and rained down at another, and in this 
process, therefore, we have agencies for multitudes of partial and 
conflicting currents, all, in their set and strength, apparently as 
uncertain as the winds. 
The better to appreciate the operation of such agencies in pro- 
ducing currents in the sea, now here, now there, first this way, 
and then that, let us, by way of illustration, imagine a district of 
two hundred and fifty-five square miles in extent to be set apart, 
in the midst of the Pacific Ocean, as the scene of operations for 
one day. We must now conceive a machine capable of pumping 
up, in the twenty-four hours, all the water to the depth of one 
mile in this district. The machine muSt not only pump up 
and bear off this immense quantity of water, but it must discharge 
it again into the sea on the same day, but at some other place. 
Now here is a force for creating currents that is equivalent in its 
results to the effects that would be produced by bailing up, in 
twenty-four hours, two hundred and fifty-five cubic miles of wa- 
ter from one part of the Pacific Ocean, and emptying it out again 
upon another part. The currents that would be created by such an 
