• The hourglass was developed to measure the passage of a unit of time.hourglass image by ?¡ãbrahim KARKINO??LU from Fotolia.com
  
  The hourglass, also called a sand glass or a sand clock, is a device that measures the passage of a block of time. Most hourglasses measure an hour, while others have been calibrated to measure as few as 30 seconds. In the Nima Sand Museum in Japan, the world's largest hourglass, containing one ton of sand, measures a full year.
  
  

Marine Hourglasses

• In the 1300s, the sand glass was used as a marine clock aboard early ships to aid in navigation. Star charts could tell seamen where they were and could provide rudimentary knowledge about direction but navigators had to know how long they had traveled on a set course in order to calculate distance. The sand in an upper globe would take one hour to run through the neck in the glass to a lower globe. By adding the number of times the glass was inverted to reset the process, the passage of time was accurately determined. The sand glass was also used aboard ship to determine when the men needed to change the watch so that each mariner had a shift of deck duty equal to those of his shipmates.
  
  

Church and State Hourglasses

• In the 1400s, monasteries used hourglasses to measure the hours between prayer so that strict adherence to canonical rule could be maintained. Sermon glasses were used in churches to keep sermons from becoming overly lengthy. Similarly, the students at Oxford university had hourglasses in the lecture halls to provide closure to sessions with long-winded professors. Medical practitioners carried pocket sand glasses to time the pulse of patients and merchants and politicians measured their working days using hourglasses to measure the time and bells to signal opening, closing and voting times.
  
  

Elaborate Hourglasses

• The rich and powerful owned elaborate hourglasses that befitted their rank and status. Charlemagne of France owned a 12-hour sand glass. Henry VIII had jewel encrusted hourglasses made for him by Holbein, a famous 16th century artist. Hourglasses were mounted in pivoting frames and outfitted with dials and pointers to mark the total number of hours passed.
  
  

Egg Timers

• The simple three-minute egg timer sold in kitchen boutiques, department stores and souvenir shops is a miniaturized form of hourglass still in use today. These tiny timepieces have also been sold as novelty items for use in board games.