gether to prosecute his
inquiries in the old region. Or old age comes on; and even although he
may have been beginning to have a few faint glimmerings as to laws and
systems in his mind, he has not the power to make much of these. He
dies; his knowledge is, to a very large extent, lost, and his log-books
disappear, as all such books do, nobody knows or cares where.

Now this state of things has been changing during the last few years.
Log-books are collected in thousands. The experiences of many men, in
reference to the same spots in the same years, months, and even hours,
are gathered, collated, and compared; and the result is, that although
there are conflicting elements and contradictory appearances, order has
been discovered in the midst of apparent confusion, and scientific men
have been enabled to pierce through the chaos of littlenesses by which
the world's vision has been hitherto obscured, and to lay bare many of
those grand progressions of nature which move unvaryingly with stately
step through space and time, as the river, with all its minor eddies and
counter-currents, flows with unvarying regularity to the ocean.

CHAPTER SIX.

TRADE-WINDS--STORMS--THEIR EFFECTS--MONSOONS--THEIR VALUE--LAND AND SEA
BREEZES--EXPERIMENTS--HURRICANES--THOSE OF 1801--ROTATORY STORMS--THEIR
TERRIBLE EFFECTS--CHINA SEAS--HURRICANE IN 1837--WHIRLWINDS--WEIGHT OF
ATMOSPHERE--VALUE OF ATMOSPHERIC CIRCULATION--HEIGHT OF ATMOSPHERE.

Before proceeding to speak of the power and the dreadful effects of
wind, it is necessary to say a word or two about the trade-winds.

It is supposed that the "trades" derived their name from the fact of
their being favourable to navigation, and, therefore, to trade. They
consist of two belts of wind, one on each side of the equator, which
blow always in the same direction.

In the last chapter it was explained that the heated atmosphere at the
equator rises, and that the cooler atmosphere from the poles rushes in
to supply its place. That which rushes from the south pole is, of
course, a south wind, that from the north pole a north wind; but, owing
to the Earth's motion on its axis from west to east, the one becomes a
north-east, the other a south-east wind. These are the north-east and
the South-east "trades." They blow regularly--sometimes gently,
sometimes fiercely--all the year round. Between the two is a belt of
calms and changeable breezes, varying from 150 to 500 miles broad--
ac