40 
STATE AGRICULTURAL SOCIETY. 
the best authorities at hand, and feel confident that they are 
not very materially out of the way. 
Beginning with spring, the season of planting and of early 
vegetable growth, the first line traced on the map, and one of 
the most interesting of all, is that which indicates a mean tem¬ 
perature of 45° Fahrenheit, for the season embracing March, 
April and May. Commencing at Hudson, on the St. Croix 
Lake, it passes successively through portions of Pierce, Dunn, 
Eau Claire, Trempealeau, Jackson, Monroe and Juneau counties, 
to Portage, and thence by a rapid southward descent to Chica¬ 
go ; thus showing that the mean temperature of spring is as 
high in the north-western part of this State, even as far north 
as Hudson, as it is at Chicago, in Northern Illinois. This is a 
remarkable fact, and when generally known cannot fail to cor¬ 
rect the erroneous impressions which now prevail as to the ag¬ 
ricultural capacity of the climate of North-western Wisconsin. 
The spring mean, of 40°, enters this State a few miles be¬ 
low Superior City, and descending in its course south-easterly, 
crosses Green Bay and Door county just above the 45th par¬ 
allel. 
The isotheral lines (lines passing through points whose sum¬ 
mer temperature is equal) are also worthy of special attention. 
It will be observed that the mean of 70° Fah., (which is the 
average temperature of Southern Pennsylvania, and of North¬ 
ern Ohio, Indiana and Illinois,) when it reaches Chicago, in its 
western course, suddenly bends northward, entering Wisconsin 
in the county of Rock, passing through Janesville and Madison, 
and thence bears north-westward to the county of St. Croix, 
whose western boundary it cuts at a point between Prescott 
and Hudson; from which it appears that the counties of Rock, 
Dane, Sauk, Monroe, Jackson, Trempealeau, and the southern 
portions of Dunn and St. Croix, have the average summer tem¬ 
perature of Chicago and ITarrisburgh. Of course the counties 
south and west of this theral line, touching Chicago, Janes¬ 
ville, Madison and St. Paul, have a still higher summer ave¬ 
rage, corresponding to Central Ohio and Western Virginia. 
The isothermal line touching places whose temperature is 
