Page:Physical Geography of the Sea and its Meteorology.djvu/225

Rh precipitation is in excess. Here, being cooled, and agitated, and mixed up with waters that are less salt, these over-heated and over-salted waters from the tropics are replenished and restored to their rounds in the wonderful system of oceanic navigation.

401. Equatorial currents.—There are also about the equator in this ocean some curious currents, which I have called the "Doldrum Currents" of the Pacific, but which I do not understand, and as to which observations are not sufficient yet to afford the proper explanation or description. There are many of them, some of which at times run with great force. On a voyage from the Society to the Sandwich Islands I encountered one running at the rate of ninety-six miles a day. These currents are generally found setting to the west. They are often, but not always, encountered in the equatorial Doldrums on the voyage between the Society and the Sandwich Islands. In Captain Pichon's abstract log of the French corvette "L'Eurydice," from Honolulu to Tahiti, in August, 1857, a "doldrum" current is recorded at 79 miles a day west by north. He encountered it between 1° N. and 4° S., where it was 300 miles broad. On the voyage to Honolulu in July of the same year, he experienced no such current; but in 6° N. he encountered one of 36 miles, setting south-east, or nearly in the opposite direction. This current does not appear to have been more than 60 miles broad. 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 water. 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 annual 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 vapour 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 vapour, 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