42 
STATE AGRICULTURAL SOCIETY. 
The explanation may be found in the tempering influence of the 
lakes, which, more slowly than the land, part with the heat 
acquired in summer, in the warm Gulf currents of air which in 
spring and summer move along up the great trough of the 
Mississippi valley, and in the cold winds from the British Ter¬ 
ritory, which in -winter gain the supremacy and sweep over the 
entire western portion of the State. The great Dividing Ridge 
running north and south, and which nearly coincides in direc¬ 
tion and position with the Fourth Principal Meridian, may also 
contribute to increase the difference between the summer and 
winter temperatures of the eastern and western portion of the 
State, by partially preventing the overflow of either the warm 
or the cold currents above mentioned. 
The mean temperature of the year is indicated on the map 
by two isothermal lines, one of 45°, the other of 40°. The 
line denoting a temperature of 45° passes near Manitowoc, 
Oshkosh, Black River Falls, and Hudson; in other words, di¬ 
rectly through the center of the State. The line of 40° crosses 
Lake Superior without touching Wisconsin. 
If we compare the temperature of the whole State in a gen¬ 
eral way with the temperature of different portions of Europe, 
we shall find our summers corresponding with those of South¬ 
ern France, our winters with those of Sweden, and of Russia 
on the Black and Caspian Seas. 
Destructive frosts seldom occur late in spring or early in au¬ 
tumn. The June or July frosts of 1859 were exceptional for 
this State, and prevailed more disastrously in Ohio and through¬ 
out the Middle States than here. 
Distribution of Moisture .—This is a question of scarcely less 
importance than that of temperature, inasmuch as the amount 
of rain may determine the cultivability of an important district, 
no matter what the basis of the soil or distribution of heat. 
But quantity alone does not determine the fertility or barren¬ 
ness of any district; if it did, some of the most barren por¬ 
tions of country would be the most fertile. Distribution 
throughout the year is also important; for, should there be a 
heavy precipitation during the winter, and yet scarcely any in 
