Climate of Middle Illinois. 23 



PEECIPITATION. 



The mean quantity of rain and melted snow was 35.6 inches per year 

 in one hundred rainy days. The smallest quantity falls in January, 1.6 in 

 seven days; the greatest in June and July, each with four inches in ten 

 and nine days The precipitation in winter is 6.1, in spring 9.7, in summer 

 11.2, in fall 8.6. This would be favorable when distributed in that way 

 every year; but the single years differ very much. In 1856 it was only 

 22.8; in 1858, 51.4. There are sometimes long droughts. From the 29th 

 of August to the 8th of October, 1871, there was only one rainy day in the 

 middle of September with 0.65 of an inch of rain. The longest period 

 without anv rain was in 1861, in October and November, which lasted, 

 twenty-eight days. There was one in the spring of 1863 of twenty-one 

 days, in April and May, 1863, of twenty days; in July, 1873, of nineteen 

 days, and the same in July and August, 1869. Sometimes there are long 

 periods of too much rain, f. e. in 1858, from the 29th of April to the 10th 

 of June, 15.7 inches in twenty-seven rainy days. 



The quantity of rain is of less importance than the number of rainy 

 days and their distribution. The highest number for one month was 18 

 in May, 1858, and in July, 1865, the lowest in September, 1871, and Feb- 

 ruary, 1877, each with one rainy day. 



5'upposing that eleven inches of rain in twenty-six days of the three 

 summer months be most beneficial, and that a plus or minus of two inches 

 and two rainy days be of no importance, than we had in the summers of 

 1862, 1869 and 1872, a great excess in quantity, viz: 9.1, 7.8 and 10.8 in- 

 ches surplus, and an excess in the number of rainy days in 1865 and 1866, 

 viz: thirteen, and seven surplus. A deficiency in quantity show the years 

 1870, 1868 and 1865 with 6.6, 5.8 and 5.6 minus, and in rainy days, 1863 

 and 1856, viz: twelve, and eight minus. 



The most normal summers (in regard of rain) were 1857 and 1871. 



The greatest quantity of rain for one month was measured in May, 

 1858, 10.64; then in June, 1872, 9.76, and in September, 1875, 9.61. 



The mean precipitation of the single months are: December, 2.5; 

 January, 1.6; February, 2; March, 2.7; April, 3.2; May, 3.8; June, 4; 

 July, 4; August, 3.2; September, 3.5; October, 2.7 and November, 2.4. 



HUMIDITY OF THE ATMOSPHERE. 



The relative humidity of the air was computed from the difference of 

 the wet and dry thermometer by means of Guyot's tables. When there 

 is no difference the atmosphere is saturated with moisture, and that is 

 noted by 100. The greater the difference the lower is the per centage; 20 

 means very dry, and there is scarcely ever noted a lower figure. 



