24 Dr. Forry on the Climate of the United States, 6fc. 



inflections of the isotheral and isocheimai lines are exhibited in 

 rapid succession, constituting two systems of climate, viz. that 

 of the Atlantic Ocean and the great lakes, which pertains, compar- 

 atively speaking, to the class of mild or uniform, and that of the 

 intervening tract and the region beyond the lakes, characterized 

 as climates emphatically excessive or rigorous. The difference 

 of climate, as the mean annual temperature is nearly the same, 

 is, therefore, owing to the unequal distribution of heat among the 

 seasons, as is well illustrated in the accompanying map. At the 

 posts on large bodies of water, the mean temperature of winter is 

 higher and that of summer lower than in the opposite localities; 

 but these results are more satisfactorily evidenced by comparing 

 the difference between the mean temperature of winter and sum- 

 mer, and the warmest and coldest month in each system of cli- 

 mate. Thus Fort Brady, at the outlet of Lake Superior, shows a 

 difference of only 42°-ll between the mean temperature of win- 

 ter and summer, while Hancock Barracks, half a degree farther 

 south, in the State of Maine, distant only one hundred and fifty 

 miles from the sea-coast, exhibits a disparity of 46°-19 ; and com- 

 paring the warmest and coldest month, the difference of the for- 

 mer is 47°-22, and that of the latter 54°-70. Again, Forts Sul- 

 livan and Snelling, in opposite systems of climate, are very nearly 

 in the same latitude, the former at Eastport, on the coast of Maine, 

 and the latter at the junction of the St. Peter's and Mississippi, 

 Iowa. At Fort Sullivan, the difference of winter and summer is 

 39°-15, and that of the warmest and coldest month, 43°-87 ; 

 while at Fort Snelling, these ratios are respectively 56°-60 and 

 6l 0, 86. Fort Howard is also in the same latitude, but as it is 

 situated at the extreme point of one of the smaller lakes, (Green 

 Bay, Wiskonsan,) the temperature is partially modified, 

 averages beins 50° 05 and 54°- 11. Next come four posts, 



these 



C3~" "~..._ 



which are nearly on the same parallel, three being of the class of 



if 



Of the former, 



two, Forts Preble and Constitution, are on the ocean, and the 

 other, Fort Niagara, is on Lake Ontario. At these posts, in the 

 order just named, the difference between the mean temperature 

 of winter and summer is respectively 41° 03, 36°-33, and 4l°73; 

 while, on the other hand, at the excessive post, Fort Crawford, 

 Wiskonsan — a point a few minutes farther south than the three 

 former — the difference is 50°-89. The results at Salem, Massa- 



