On clear, cloudless nights, the earth loses its heat more quickly than on cloudy nights. Therefore, the earth and the atmosphere get cooler much sooner.
Since cooler air usually brings a heavy dew, you can be pretty sure that when you see a heavy dew, the sky is clear and therefore good weather lies ahead.
But in most places, even the heaviest dew is not really very heavy. In London, for instance, the total amount of water deposited in the form of dew is less than 11/2 inches a year, and in other places, it’s less than a quarter-inch!
In some tropical places, the dew is so heavy that it collects in gutters, just like rain!