es the stream to the fact, that the earth being a globe, the water
on the equator is higher than that of the tropics, and the lower stratum
of fluid circles round constantly in its endeavour to reach into the
bigger volume beyond its reach; but I can't say much for this theory
myself, Tom."

"But how do you know the Gulf Stream from the rest of the ocean?" I
here asked.

"As easily as you can distinguish a marlinespike from a capstan-bar,"
answered Captain Miles. "It is not only bluer than the surrounding
water, through which it flows, as I've told you, like a river, but it is
also several degrees warmer; for, when a ship is close to the stream and
sailing in the same direction in which it is running, a bucket of water
dipped from the sea on one side of the vessel will show an appreciable
difference of temperature to that procured from the other. Besides, my
boy, there's the Gulf-weed to tell you when you are within the limits of
the current; however, you'll see lots of the weed by and by, no doubt,
before we finish our voyage."

"You said, captain," I observed, "that the great currents of the ocean
are produced by the trade-winds?"

"Undoubtedly," he replied. "Blowing with regular force on the surface
of the sea, they cause it to move in the same direction in which they
are travelling; and, this motion once acquired, the ocean stream keeps
up its course far beyond where its original propelling power directly
acted upon it. The `Great Equatorial Current' is produced by the south-
east trade, the Gulf Stream, as I've just explained to you, by the
western or passage winds; and the branch of the latter current that
skirts the British Isles and Southern Europe, until it falls in again
with the northern portion of the Equatorial Current, by the north-east
trade-winds. Thus, the circle is completed, the water being ever in
motion round the centre of the tropic of Cancer, just in the same way as
the winds of this region are."

"But what causes the trade-winds?" I next asked.

"You young rascal!" said Captain Miles, shaking his fist at me in a
jocular manner, "I'll have you keel-hauled if you utter another
question! I will answer you this one, however--but it is the last time,
though, mind that! The sun, my lad, is the source of the winds of the
globe, as it is the prime agent of heat and life. The atmospheric air
being heated by the solar orb at the equator, where its force is
necessarily the greatest, ascends