Hourglasses, How they came to come

 Introduction

      An hourglass is a object used for measuring time with usually sand. There are many possibilities for how much time is holds. It's factors are: how much sand, what type of sand, diamter of the orifice, and the volume of the hourglass.
      Appearance
   The hourglass is also known as the sandglass. It could have been introduced by 8-century monk named  Luitprand. It was not after is while in the 1300's that the fresco Allegory of Good Government, while Temperance is holding a basic hourglass, in 1338 by Italian painter Ambrogio Lorenzetti (1290-1348).
  Competition
      The hourglass was popular during this time,  it was better than the clepsydra, temperatures did not affect the hourglass, unlike the clepsydra.
       In the eighteenth century Ferdinand Magellan had used 18 hourglasses per ship while he was circumnavigating the globe.
   Formula  
       In 1996, a few British reasearchers from the University of Leicester found a equation on an hourglass. Ballotini gave good results for there formula for the time that it takes to fall (period).The aperature has to at least be 5 times the particle diameter. Here is the formula:

P=KV(D-d)^-2.5

P - Period

K - depends on the shape of the reservoir, the researchers found different values for K for conical container shapes and hourglass shapes.

V- bulk volume of the ballotini

d - maximum bead diameter in millimeters

D - the diamteter of the circular orifice in millimeters

Large Hourglasses

There was a 39ft. hourglass built in 2008 in Moscow, Russia. Charlemagne of France had a 12 hour hourglass which he enjoyed. Holbein, the artist, made a hourglass for Henry the VIII of England.

You Try!

    This formula is helpful, but sort of hard to figure out. If you are good at math and have a opening/closing hourglass with ballotini, try it out!