A Sound

When someone on an island or near the sea on a mainland speaks of a "sound" they mean a bay that has a measured bottom by using an old lead line. Sounds are places where the roughest waves are broken up by reefs and anchors can catch ground, so moored boats can find a degree of safety there compared to "no sounding" areas where the full brunt of the weather must be taken.

The lead (or steel) weight was dropped with a rope attached and the sounder called the mark...giving us of course Mark Twain...for mark two fathoms (12 feet). The story is I think more complicated than that, but I'll leave that for Mark Twain fans.

If the sounder reached the end of his rope (giving us...I'm at the end of my rope!) and there was no sounding...the thud of the weight hitting bottom, the sounder called "no sounding." As soon as islands came into view from a crow's nest, the sounder started work. This was at once a way of navigating by sounding charts and also a way of protecting a ship from running aground.

See, http://en.wikipedia.org/wiki/Sounding_line