The main land-mass of the United States is in the temperate zone, and the climatic conditions of the whole country are about what is general in such zones modified chiefly by the great mountains and the winds. With every variation of surface it possesses every variety of climate, from that of the tropics to that of the Arctic regions. It is at the same time one of the hottest and one of the coldest countries; one of the wettest and one of the driest. The prevailing winds are from the west and are an important factor in the climatic conditions. The circulations of air from west to east does not take place in steadily blow ing winds, as is the case with the trades, but in cyclonic or whirling storms that have. a gen eral easterly movement alternating with anti cyclonic movements of a similar character. In these storms winds blow from all directions, the general course being nearly toward the centre of the storm. There is another class of storms which occur not infrequently, al though they do not form part of the regular air circulation. This is what is commonly known as the West Indian hurricane, irery vio lent and of a much more intense type than the ordinary cyclone of temperate latitudes. Originating in the tropics, their course is gen erally over the West Indies, entering the United States on the Gulf Coast and working off to sea in a northeasterly direction. Many of these have been extremely disastrous. The
average annual temperature of the extreme southern part is 75° F. and of the extreme north 45°. The average temperature for Jan uary in the extreme north (exclusive of Alaska) is about 20'; for July about 60°. The mercury falls as low as 40° below zero in the northern part of Minnesota, and is some times as high as 120° in the hot, dry sections of Arizona and Texas. The west winds, which are prevalent in January, and which sweep over large interior areas lower the tem perature, frequently to the minimum. The dif ference in temperature of places in the same latitude on the Atlantic and Pacific Coast is quite marked. That of the Pacific is much warmer than that of the Atlantic. The rain fall is generally the greatest in Washington, Oregon and Florida, but the humidity is great in the southern portion of Louisiana and other places along the Gulf Coast. The region around the Great Lakes has not an excessive humidity; but it is subject to extreme and rapid changes in temperature. This region is also subject to extreme changes in the winds. The Mississippi Valley receives its rainfall al most entirely from the Gulf while the Atlantic States are supplied from the Atlantic Ocean. It is estimated that the Gulf supplies fully 55 per cent of the total rainfall in continental United States, the Pacific• Ocean 30 per cent and the Atlantic 15 per cent. See AMERICA