Edmund Halley

“ But whatever is the true cause, it is in fact certain, that warmth does separate the particles of Water and emit them with a greater and greater Velocity as the heat is more and more intense, as is evident in the steam of a boiling Cauldron, wherein likewise the Velocity of the Assent of the Vapours does visibly decrease till they disappear, being dispersed into and assimulated with the Ambient Air. ”

“ Many of these again meeting in one common Valley and gaining the plain Ground, being grown united in one common Channel make such streams as the Rhine, the Rhone, the Danube, which latter one would hardly think the collection of Water condensed out of Vapour, unless we consider how vast a Tract of Ground that River drains, and that it is the sum of all those Springs which break out on the South side of the Carpathian Mountains, and on the North side of the immense Ridg of the Alps, which is one continued Chain of Mountains from Switzerland to the Black Sea. ”

“ If the difference between Rain and Dew, and the cause why sometimes ‘tis Cloudy, at other times Serene, be enquired, I can offer nothing like a proper solution thereof, only with Submission to propose Conjectures which are the best I can find, viz. That the Air being heap’d up by the meeting of two contrary Winds, when the Mercury is high, the Vapours are the better sustained and kept from Coagulating or Condensing into Drops, whereby Clouds are not so easily generated: and in the Night the Vapours fall down single as they arose in the imperceptible Atoms of Water. ”