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valley. Isotherms travel around the upper edge of such 

 places. But they travel around the lower edge of a mountain 

 chain. A decided bend to the southward, therefore, means 

 that a chain of mountains bars the line of equal heat, which 

 is deflected, or turned out of its course, by the obstruction. 

 Near the seacoast the isotherm may turn either up or down. 

 A warm ocean current with warm, moist winds will turn the 

 isotherm upward, as on the Pacific coast; the outswinging of 

 the Gulf Stream from the Gulf of Maine turns the isotherm 

 downward and gives the cool summers of the New England 

 coast. The temperature line may be thought of as like a tiny 

 cobweb attached at both ends and driven up and down by 

 Warm winds or cold, or turned out of its course by obstructions 

 that would cause a change of temperature. Thus it may be 

 that a place far to the north and one far to the south may 

 have the same climate, one isotherm passing through both. 

 But it is not only winds, currents, and distance north 

 that make temperature. There must be some reason why a 

 mountain chain will deflect the isotherm. Why is it? We 

 know very well that the top of a mountain is cooler than the 

 valleys about it, not only because it feels every breeze, but 

 because it is higher. We can see that it is cooler than the 

 country round about, for the snow lies upon its top long 

 after it has disappeared from the valleys, and the higher 

 the mountain the longer the snow lingers. Thus we infer 

 that temperature decreases with elevation. Places of the same 

 latitude and having the same level above the sea, if there 

 were no disturbing influences, would have the same climate. 

 There would be one climate at sea-level, another at two 

 thousand feet above, another at five thousand, and so on, 

 every few hundred feet showing more or less difference in 

 climate. In a single lone and lofty mountain we should find 



