A Droplet Puzzle

Kevin Kilty

On a recent morning I stepped out of my house to greet the day, and noticed two droplets that had fallen from my rain gutter onto the table on the porch. Figure 1 is a photograph of these droplets as I found them.

Figures 1 and 2. Two views of the two droplets described in the text.

One droplet is about 3 mm high and 10 mm in diameter, and the other is 3 mm in diameter and 1 mm high. Around each is a nearly perfectly circular splatter, yet each droplet has pulled back into a dome-shaped bead of water that sits at or near the center of the splatter.

How can the droplet appear to wet the table as a splatter yet also form a bead at the center? The solution to this mystery was immediately apparent when I touched the splatter just outside the bead. Would readers like to speculate on what I found, and explain this observation?

Other important pieces of information are:

1) I had just recently (the day before in fact) applied the last of four coats of spar varnish to the table (the varnish had more than 12 hours of time to dry completely before nightfall), and

2) there was a heavy fog during the night, which was the reason for the droplets in the first place.


Readers, please send your explanations for this phenomenon to "Backscatter." Place "Droplet" in the subject line. Editor.