quator and the tropic of Cancer: and it reaches from
the east coast of Africa to the coasts of India, China, and the
Philippine Islands. Its influence extends sometimes into the Pacific
Ocean, as far as the Marcian Isles, or to longitude about 145 east;
and it reaches as far north as the Japan Islands. The north-east
monsoon prevails from October to May, throughout nearly the same
space, that the south-west monsoon prevails in during the former
season. But the monsoons are subject to great obstructions by land;
and in contracted places, such as Malacca Straits, they are changed
into variable winds. Their limits are not everywhere the same; nor
do they always shift exactly at the same period, but they are
generally calculated upon about the times I have mentioned."

EMMA. "Mamma, are not trade-winds something like monsoons?"

MRS. WILTON. "So far similar that they are confined to a certain
region, and are tolerably regular in their operations. The
trade-winds blow, more or less, from the eastern half of the compass
to the western. Their chief region lies between the tropics from
23-1/2 north to 23-1/2 south latitude, although in some parts of
the world they extend farther; but it is only in the open parts of
the Pacific and Atlantic Oceans that the true trade-winds blow.
These winds shift many degrees of latitude in the course of the
year; but skilful navigators usually know where to catch them, and
make them serviceable in helping to blow their richly laden vessels
'o'er the glad waters of the bright blue sea.'"

GEORGE. "Do you know the cause of these regular winds, papa? You say
learned men try to discover _why_ such things are so, and generally
find out _causes_ from their effects."

MR. WILTON. "Exactly so, my boy; and learned _women_ do the same: as
an instance, I will quote the learned Mrs. Somerville on this very
subject, and give you an excellent reply to your question.

"'The heat of the sun occasions the trade-winds, by rarefying the
air at the equator, which causes the cooler and more dense part of
the atmosphere to rush along the surface of the earth to the
equator, while that which is heated is carried along the higher
strata to the poles, forming two currents in the direction of the
meridian. But the rotatory velocity of the air corresponding to its
geographical situation, decreases towards the poles; in approaching
the equator it must therefore revolve more slowly than the
corresponding parts of the