The word monsoon is probably derived from an Arabic word meaning "seasons." It is a peculiarity of this monsoon that in summer it blows in a northeasterly direction from the sea and in the winter in a southwesterly direction from the land. This divergence from a direct north and south is caused by the rotation of the earth and the explanation is the same as that we have given for the trade winds.
In the southern latitudes there is a comparatively constant condition of wind and weather, because the surface of the globe in these regions is mostly water; but in the north, where most of the land surface is located, we have a very different and a very complicated set of conditions, as compared with the southern zones.
The freaks of wind and weather that we find prevailing upon the North American continent are not so easily accounted for as the phenomena heretofore discussed. In the northern part the land reaches far up toward the north pole, while on the west lies the Pacific Ocean, which merges into the Arctic Ocean at Bering Strait. The climate of the western coast is affected by a warm ocean current that sets up as far north as Alaska, while high ranges of mountains prevent the effects of this warm current from being felt inland to any great extent; all of which helps to complicate any theory that may be advanced regarding changes of weather. Aside from the changes of temperature that are due to the seasons, which are caused by the oscillating motion of the earth between the limits of the Tropic of Cancer on the north and the Tropic of Capricorn on the south, there are other changes constantly taking place in all seasons of the year. While it is not difficult to account for the change of seasons and the gradual change of temperature that would naturally follow--owing to the difference of angle at which the sun's rays strike the earth--it is more difficult to account for the violent changes that occur several times during the progress of a season, as well as the less violent ones that come every few days. In fact, it rarely happens that the temperature is exactly the same on any two successive days during the year. The diurnal changes are easily accounted for by the rotation of the earth on its axis each day. But there is another class of phenomena with which the "weather man" has to struggle when he is making up a forecast of the weather from day to day.