This lovely antique sand glass consisted of an inner glass bulb filled with sand or similar enclosed in a wooden cage. It measures approx 19cm in height x 9.5cm w These timers were made in various sizes for different requirements but the usual length of time was an hour, half hour or 3-4 minutes.This one  from the late 18th century/ early 19th century takes approx an hour to run through. These were often used by the Royal Navy up until 1839  and for marines as a dependable measure of time whilst at sea. It has also been documented that these timers were used in the church pulpit for measuring the parsons sermon to ensure it did not overrun what a good idea.!!!!!