A candle flame seen at 30 miles on a dark, clear night.

The tick of a watch under quiet conditions at 20 feet.

One teaspoon of sugar in two gallons of water.

One drop of perfume diffused into the entire volume of a three-room apartment.

The wing of a bee falling on your cheek from a distance of one centimeter.

Galanter E. Contemporary psychophysics. In: Brown R et al, editor. New directions in psychology. New York: Holt, Rinehart and Winston; 1962.