VOL. XLI.j PHILOSOPHICAL TRANSACTIONS. 449 



temperament to another, must be affected in the same manner also : so that 

 vapour, carried from a colder to a warmer air, will ascend ; and, on the con- 

 trary, vapour carried from a warmer to a colder air, will descend. 



Now if cold condenses the air, and thereby makes it press on the warmer ; 

 and if vapour, carried by a stream of air from a colder to a warmer region, 

 ascends; we have the reason why the north-east blows, and why it blows dry. ' 



Let us fix upon some spot in the continent of North-Europe, whence this 

 wind comes to us : suppose Archangel, which lies on our north-east point, and 

 is in 65 degrees northern latitude: when the frost is intense, the incumbent 

 air there must needs be very heavy ; that air will press every way : qua data 

 porta, ruit. Let us consider which way this condensed air can burst out from 

 thence : it cannot go to the north, where the cold is greater ; nor to the east, 

 for the air over the large continent of Tartary is at least of equal coldness with 

 itself. To the west, the air might find a free passage over the ocean, were not 

 the colds of North-America too near. The main outlet is between both, to- 

 wards the Atlantic-Ocean : the warm air over which being able, of itself, to 

 make but a feeble resistance, yields to the superior force; the conqueror eagerly 

 pursues his victory, and we, happening to lie directly in the way, feel then a 

 cold dry north-east wind : this is the wind that brings us frost in the winter. 

 When the winter is severe, it continues to blow all the spring, and its influence 

 reaches to the end of the summer. 



This it seems sufficiently proves, that air, flowing from a cold to a warmer 

 quarter, will blow dry : but, like a willing witness, it proves too much ; for, if 

 wind proceeds only from cold air pressing on hot, and if heat makes the vapour 

 ascend, it follows from thence, that wind can never bring rain ; whereas we 

 find the contrary by sad experience. 



How can this be accounted for, on the principles commonly received ? That 

 vapour, wafted from a warmer to a colder region of air, should precipitate, is 

 what we have already shown. But the question is, why does the south-west 

 blow ? What is the cause why a stream of air should be carried, for so long a 

 time, and with so great violence, as we have often felt, from a warmer to a 

 colder, from a rarer to a denser, from a lighter to a heavier quarter ? To the 

 north-east of us lies the continent of North-Europe, great part of which is, in 

 the winter, deprived of the sun's heat, and consequently very cold ; on the 

 other side, to the south-west, lies the vast Atlantic ocean. We find by ex- 

 perience, that the sea-shore is warmer than the inland ; that the sea is warmer 

 than the shore; and that the ocean is still warmer than the sea. Besides, the 

 more you go from hence towards the south, the nearer you go to the sun ; and 

 the more north, the farther from it : this must make the south-western ocean 



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