This lovely antique sand glass consisted of an inner glass bulb  filled with sand or similar  enclosed in a wooden cage. It measures approx 11.5cm in height x 7cm.They were made in various sizes for different requirements but the usual length of time was an hour, half hour or 3-4 minutes.The larger one from the late 18th century/ early 19th century takes approx 30 minutes to run through. These were often used by the Royal Navy up until 1839 to count in half hours and for marines as a dependable measure of time whilst at sea. It has also been documented that these half hour timers were used in the church pulpit for measuring the parsons sermon to ensure it did not overrun what a good idea.!!!!! Also  these antique timers were used for measuring labourers break times!!The small antique sand glass timer in image two takes approx 3 minutes 30 seconds to run through used mainly as an egg timer these smaller ones began to replace the larger timers as they were more convenient to use.