A Guide To The Scientific Knowledge Of Things Familiar Part 66

A. Yes. As pa.s.sing clouds screen the direct heat of the sun from the earth, they diminish the _rarefication of the air also_: and this is _another_ cause why neither the strength nor direction of the wind is _uniform_.

Q. _Would the winds blow regularly from east to west, if these OBSTRUCTIONS were REMOVED?_

A. Without doubt they would. If the whole earth were covered with _water_, the winds would always _follow the sun_, and blow from east to west. Their irregularity is owing to the interspersion of _sea and land_, and the irregularities of the earth's surface.

Q. _Do winds NEVER blow REGULARLY?_

A. Yes; in those parts of the world, where these obstructions do not exist; as on the Atlantic and Pacific Ocean, the winds are pretty uniform.

Q. _What are the winds, which blow over the ATLANTIC and PACIFIC Ocean, called?_

A. They are called "Trade Winds."

Q. _Why are they called TRADE WINDS?_

A. Because (as they blow uniformly in one direction) they are very convenient to those who _carry on trade_ by means of these oceans.

Q. _In what DIRECTION do the TRADE WINDS blow?_

A. That in the _northern_ hemisphere blows from the _north-east_: that in the _southern_ hemisphere from the _south-east_.

Q. _Why do they not blow from the FULL NORTH and SOUTH?_

A. Because the _polar current_, combining with the _equatorial current_, give the wind a _new direction_.

Q. _What is the CAUSE of the EQUATORIAL current?_

A. The rotation of the earth upon its axis.

Q. _What is the cause of the POLAR CURRENT?_

A. As the heat in the _torrid zone_ is always _greatest_, and at the _poles_ the _least_, therefore a constant current of air rushes _from the poles_ towards the _equator_.

Q. _How does the COMBINATION of these two currents give a new direction to them both?_

A. When these currents of air meet at the equator, they _clash together_, and fly off in a new direction.

Q. _Do trade winds blow from the north-east and south-east ALL the YEAR ROUND?_

A. Yes, _in the open sea_; that is, in the Atlantic and Pacific Oceans for about 30 degs. each side of the equator.

Q. _Do the TRADE WINDS blow uniformly from north-east and south-east in the INDIAN OCEAN?_

A. No; nor yet in those parts of the _Atlantic_ and _Pacific_ which _verge on the land_.

Q. _Why do not the trade winds blow uniformly from north-east and south-east in the INDIAN OCEAN?_

A. Because when Arabia, Persia, India, and China, are exposed to the enormous heat of their summer sun, the _air is so rarefied_, that the colder air from the south pole rushes _towards these nations_, and not to the _equator_; in consequence of which, a SOUTH-WEST wind is produced for _six months of the year_.

Q. _How does it blow for the OTHER 6 months?_

A. When the sun has left the _northern_ side of the equator for the _southern_, then the _southern part of the torrid zone_ is most heated; and the cold air from the north (rus.h.i.+ng towards the southern tropic) is diverted to the NORTH-EAST, where it continues for the _other_ six months of the year.

Q. _What are the six-month trade winds called?_

A. They are called MONSOONS; and blow from the _north-east_ from September to April, and from the _south-west_ for the _other_ six months of the year.

Q. _Have WE any regular winds in ENGLAND?_

A. No; our island (having a _continent on one side_, and a _sea on the other_) has a most _variable_ climate.

Q. _Have the winds in England NO general direction throughout the year?_

A. We generally find that _easterly_ winds prevail during the _spring_ of the year, and _westerly_ winds are most common in the _summer_ and _autumn_.

S-West winds are most frequent in July and August. N-East winds in January, March, April, May, June; and most seldom in July, September, and December.

Q. _When are the WINDS in ENGLAND generally the HIGHEST?_

A. The winds in December and January are generally the highest. Those in February and November the next; and those in August and September the least boisterous.

Q. _Why are the winds of Europe generally HIGHEST in DECEMBER and JANUARY?_

A. Because the sun is _furthest south_ in those months; and (as the heat in these northern regions rapidly _decreases_) the _contrast between our temperature_ and that of the _torrid zone_ is greater in December and January, than in any _other_ two months throughout the year.

Q. _Why does this CONTRAST of heat increase the VIOLENCE of the WINDS?_

A. As the air always seeks to _preserve an equilibrium_, therefore the _greater the contrast_, the more violent will be the rush of air to _equalize_ the two volumes.