40 The Climate of Peoria. 
How great the influence of insolation must be upon the growth of plants is 
shown by the difference of the thermometer in the shade and exposed in the 
sun, which in June exceeds 20 degrees and more yet in winter. 
WIND. 
West winds are prevalent from October to-April; south winds during the 
summer; only in August east equals the south. About 12 for each 1000 of ob- 
servations are marked as high winds, gales or hurricanes; but the force of 
winds were not measured by the anemometer, but only estimated, and the 
dates are not quite reliable. The windiest months are March and April, the 
calmest August and September. 
Wind and temperature, wind and cloudiness, wind and precipitation are in 
a certain degree correlative. The warmest winds are south, southwest and 
east; the coldest northwest, north and northeast; the difference between the 
coldest and warmest winds is about 15, in spring even 20 degrees. Above the 
average is the temperature with south and southwest in all the months, with 
east only in the spring and fall. Southeast wind is too scarce, so that no 
reliable mean could be abstracted. The temperature of north is always below. 
Northeast is only in November, December and January above, and that may 
be accounted for by the great quantity of cloudiness that always accompanies 
these winds preventing radiation. Northwest has only in August a tempera- 
ture above average. ‘The region from which this wind comes, is naturally a 
cold one, only during the summer months excessive heat is accumulating, 
which has the above effect upon these winds. The same reason is good for the 
west during all the summer months; in the rest the west winds are cooler. 
Northeast brings the most cloudiness and west the least; the west is the 
only one that has a cloudiness considerably below the average. 
The relation of wind and precipitation must be considered in a double way. 
when we compute the direction of wind in 1000 observations of precipitation, 
then we find that we have 258 times south wind, 174 times east, 159 times 
northeast, 105 times southwest, 95 times west, 84 northwest, 79 north, and 46 
times southeast. But when we reduce the observations of precipitation to 
1000 of each wind direction, then we find for each wind the following per 
mille of rain observations: Northeast 317; southeast 153; southwest 132; 
south 126; northwest 124; east 111; north 98; west 46. That shows that 
northeast is the prevalent rain wind. But the single’ months differ. In sum- 
mer southwest brings the most rain, and nearly all the thunderstorms come 
southwest, west or northwest. The average number in a year is 28. 
