_Climate._--The climate of Illinois is notable for its extremes of temperature. The warm winds which sweep up the Mississippi Valley from the Gulf of Mexico are responsible for the extremes of heat, and the Arctic winds of the north, which find no mountain range to break their strength, cause the extremes of cold. The mean annual temperature at Winnebago, near the N. border, is 47° F., and it increases to the southward at the rate of about 2° for every degree of latitude, being 52° F. at Springfield, and 58° F. in Cairo, at the S. extremity. The lowest temperature ever recorded in the state was -32° F., in February 1905, at Ashton in the N.W. and the highest was 115° F., in July 1901, at Centralia, in the S., making a maximum range of 147° F. The range of extremes is considerably greater in the N. than in the S.; for example, at Winnebago extremes have ranged from -26° F. to 110° F. or 136° F., but at Cairo they have ranged only from -16° F. to 106° F. or 122° F. The mean annual precipitation is about 39 in. in the S. counties, but this decreases to the northward, being about 36 in. in the central counties and 34 in. along the N. border. The mean annual snowfall increases from 12 in. at the S. extremity to approximately 40 in. in the N. counties. In the N. the precipitation is 44.8% greater in spring and summer than it is in autumn and winter, but in the S. only 26.17% greater. At Cairo the prevailing winds are southerly during all months except February, and as far north as Springfield they are southerly from April to January; but throughout the N. half of the state, except along the shore of Lake Michigan, where they vary from N.E. to S.W., the winds are mostly from the W. or N.W. from October to March and very variable for the remainder of the year. The dampness and miasma, to which so many of the early settlers' fatal "chills and fever" were due, have practically disappeared before modern methods of sanitary drainage.