Description
This glass has been repaired in such a way that its running time cannot now be measured, but from its dimensions is probably a four-minute glass, that is, turned over, with the upper glass full, it takes four minutes for all the sand to run into the bottom glass.

Such simple methods of marking time were used when ‘streaming’ the ship’s log. The wooden log, attached to its rope, was thrown overboard; the frame was set with the upper glass full, and the rope was paid out as the ship sailed forwards. When the upper glass was empty, the sailor measured the length of rope paid out during that two minutes. From this, he could calculate the ship’s speed in nautical miles (knots) per hour.

04/08/2008
Created by: Dr Anita McConnell on 04/08/2008