Hourglass - the invention that changed the attitude of the person at the time.History does not give a clear answer about their origin, however, it can be assumed that a similar device was known in ancient Asia BC.
Once a simple yet highly mobile means of measurement of time - they quickly spread in the Middle Ages and became the perfect complement to the popular at the time sundial.
Hourglass allowed to measure time during dusk and were much more accurate clepsydra.A special place is occupied by the watch on ships, aspitching did not render such a large impact on the pour sand in contrast to the water clock.In the first place with their help it was determined by the speed of the ship - was dumped in the water rope with knots and 30-second clock to measure time.At the same time inverting clock sailors lowered a rope into the water begins to count, often to the touch, "nodes" - hence there was speed in knots.Also, the ships used four hours hourglass, using them to pinpoint the time derzhurstva watch one team.
The main drawback of the hourglass was a small amount available to measure the time interval.So, it was the most popular watch, measure an hour or two, sometimes three hours.On the production is also often used to measure out the clock, eight or twelve of hours - the duration of the working day.
accuracy of hours depends primarily on the quality of the sand.Normally I used the same sand that went to the manufacture of glass - the annealed, fine-grained and sifted through a fine sieve.Instead of sand could also be used finely grated shell or shells crumbling marble.Also hourglass accuracy depends on the quality of the surface of the glass used, so over time due to abrasion of internal surfaces of glass sand such a clock accuracy falls.
In the 18th - 19th centuries, with the advent of factories and plants, as a result of cheaper production, widespread, once expensive and bulky mechanical watches and alarm clocks.As a result - the hourglass were ousted from everyday use, but despite that even today they are widely used in industry, medicine and many other areas.
