170 HISTORY OF 



In this manner, the sea supplies sufficient hu- 

 midity to the air for furnishing the earth with all 

 necessary moisture. One part of its vapours fall 

 upon its own bosom, before they arrive upon land. 

 Another part is arrested by the sides of moun- 

 tains, and is compelled, by the rising stream of 

 air, to mount upward towards the summits. Here 

 it is presently precipitated, dripping down by the 

 crannies of the stone. In some places, entering 

 into the caverns of the mountain, it gathers in 

 those receptacles, which being once filled, all the 

 rest overflows ; and breaking out by the sides of 

 the hills, forms single springs. Many of these run 

 down by the valleys or guts between the ridges of 

 the mountain, and, uniting, form little rivulets or 

 brooks ; many of these meeting in one common 

 valley, and gaining the plain ground, being grown 

 less rapid, become a river; and many of these 

 uniting, make such vast bodies of water as the 

 Rhine, the Rhone, and the Danube. 



There is still a third part, which falls upon the 

 lower grounds, and furnishes, plants with their 

 wonted supply. But the circulation does not rest 

 even here ; for it is again exhaled into vapour by 

 the action of the sun and, afterwards returned to 

 that great mass of waters whence it first arose. 

 This, adds Dr Halley, seems the most reason- 

 able hypothesis ; and much more likely to be true 

 than that of those who derive all springs from the 

 filtering of the sea waters through certain imagi- 

 nary tubes or passages within the earth ; since it 

 is well known, that the greatest rivers have their 



