INTRODUCTION. 
73 
starting from the southeast corner of this State sweeps down through the 
southern half of Georgia and Alabama, many miles below Montgomery, 
and in fact touches Mobile Bay (isotherm 65°. 8), and crossing the Mis- 
sissippi a little above Natchez, makes a southward bend by Austin, Texas, 
and after a slight upward curve reaches the eastern escarpment of the 
great western plateau, and then “ runs down the longitude” into Mexico, 
making its final appearance in southern California on the Pacific coast. 
The other line, of 45°, starting on the coast at Portland, Maine, and 
bending gently southward until it touches the northern edge of western 
Masschusetts, makes a sudden sweep to the north through Lake Cham- 
plain into the valley of the St. Lawrence, and then trends west a little 
south along the northern coast of Ontario, by Toronto, across the middle of 
Lake Michigan, and again with a northwest sweep through St. Paul, rises 
quite into the British Dominion in the valley of the Sascatchewan, beyond 
the parallel of 50° ; and only after reaching the flanks of the Rocky 
Mountains does it touch, by a sudden southward plunge, the latitude of 
the Grandfather Mountain. So that these two lines enclose almost the 
whole United States and a portion of British America and Mexico. 
The mean for the State, which is nearly 59°, if mapped, would enter 
its territory from Virginia, in Granville county, and leave it in Mecklen- 
burg, and after making a wide curve into South Carolina and Georgia, 
around the southwestern end of the Appalachians, return to the par- 
allel of 36-J 0 about midway of the State of Tennessee. 
If the geography of this line be traced through Europe and Asia, it 
will give a clue to still wider climatic relationships. It touches the Eu- 
ropean coast a little north of Lisbon, and passing through Madrid, hugs 
the upper coast of the Mediterranean round by Genoa, and bearing down 
through middle Italy by Florence, turns again east by Constantinople, 
Trebizond, and on through the heart of China, passing near Shanghai, 
reaches the Pacific in the latitude of southern Japan. And if the two 
extreme isotherms of the State, say only 48° and 66°, be followed around 
the globe, they will be found to enclose a zone within which lie nearly all 
the great centres of the population and power and civilization of the hu- 
man race, both ancient and modern, in the old world and the new. But 
climate, even so far as dependent on temperature, is not wholly expressed 
by the annual isotherms. On the contrary, as long since pointed out by 
Humboldt, a most “ important influence is exercised on vegetation and 
agriculture, on the cultivation of fruit, and on the comfort of mankind, by 
differences in the distribution of the same mean temperature through the 
different seasons of the year.” “ If in a thermic scale of different kinds 
of cultivation, we begin with those plants which require the hottest cli- 
19 
