India lies directly north of the great Indian Ocean, and the lower part of it comes within the tropical belt lying south of the Tropic of Cancer. During the summer season here the earth stores more heat during the day than it radiates or loses during the night. This causes the wind to blow in a northerly direction from the sea both day and night for six months each year, from April to October. During these months the land is continually heated day and night to a higher temperature than the water in the ocean south of it. The winds are probably not so severe during the night as through the day, as the difference between the temperature of the land and the water will not be so great during the night; and difference of temperature between two points usually means a proportional difference in the velocity of the wind. There is a time in the fall and spring, while there is a struggle between the temperature of the land and water for supremacy, when the winds are variable, attended with local storms somewhat as we have them in the temperate zone. But after the sun has moved south to a sufficient extent the land of India loses more heat at night than is stored up in the day; hence the conditions during the winter months are reversed, the water is constantly warmer than the land, and there is a constant wind blowing from the land to the ocean, which continues until April, when after a season of local storms the conditions are established in the opposite direction. These winds are called "monsoons." 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.