The whole of Siam lies between the Tropic of Cancer and the Equator and is subject to the typical monsoonal climate of southeastern Asia, by which the prevailing winds, from the latter part of April to the middle of October, consistently blow from the southwest and from mid-October to April, from the northeast. In Northern, Central, and Eastern Thailand there are three distinct seasons--the hot weather, the rains, and the cold weather, the first extending from February or March to May, the second from June to October, and the third covering the remaining months of the year. When the northeast winds blow strongly, the cold weather is very marked, but at such times as the seasonal winds fail, the cold weather is scarcely distinguishable from the hot. In Northern Siam, which lies at greatest distance from the sea and possesses greater radiation, the days may be hot even during the cold weather when the night temperatures afford a strong contrast by dropping to as low as 50° F. and on the mountains even lower, although never reaching freezing temperatures. The basin of Eastern Siam, with its thin vegetation and cut off from cooling breezes by its surrounding rim, is subject to terrific heats during the day and, during the winter, very low temperatures at night. The central plain, outside of Bangkok, is pleasantly cooled during the hottest season by the continuous sea winds, night and day; in Bangkok, however, perhaps owing to houses of masonry in place of thatch and the drainage of surrounding marshes, the climate is not only appallingly hot but actually becoming perceptibly more so year by year. Peninsular Siam has the mildest and most equable climate, the greatest annual rainfall, and only two noticeable seasons--the hot weather from February to August and the rains from September to January, with the peak of the wet season coming in December.