Dew It
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In the late 1700's, the likes of Isaac Newton, Benjamin Franklin, Noah Webster, and Charles Darwin among others were waging a mini battle about the nature of a very benign form of weather -- dew. I'm meteorologist Dave Thurlow from The Mount Washington Observatory and this is The Weather Notebook.

Galileo Galilei

The problem, or the question back in the early days of meteorology, was quite simple -- where does dew come from. I"m sure you"ve experienced days even in the desert where you go outside first thing in the morning and the ground is wet, or if it's cold enough the ground is frosty. You know it didn't rain or snow, but there it was -- wet ground.

To many of the 18th century's great thinkers, this was a true puzzle. The debate centered around two possible sources of dew and frost, both of which it turned out to be wrong. One was that dew "seeps" up or rises from the ground, and the other was that it "falls" imperceptibly from the sky. It turned out here, as well as in much of science, that close observation was the down fall of these theories.

It was observed that dew didn't form under trees -- or on cloudy nights -- so another mechanism had to be found. In 1812, William Wells, an American born doctor working in London, found that the ground loses heat to space, allowing it to cool to the dew point, the point at which water vapor next to the ground condenses into dew or frost. So the dew wasn't rising from underground OR falling from the sky, it simply appeared out of thin air -- much like the sound of my voice right here on The Weather Notebook, funded by The National Science Foundation, and underwritten by Subaru -- the beauty of All-Wheel Drive.