Hourglasses

Sand hours are a device which is well - known to each person. Its use began long before emergence standard and habitual to everyone - a mechanical clock. Hourglasses, as well as any other, are created for measurement of time.

Hourglasses - the special device for counting of periods consisting of two vessels connected by a narrow mouth, one of which is partially filled with sand. Time for which sand through a mouth is poured into other vessel can make from several hours to several seconds. Presently hourglasses which measure 1, 2, 3, 5, 10, 15 and 20 minutes are popular.

Hourglasses apply at schools, in medicine, in different laboratories, at plants and many other enterprises. All appreciate their accuracy, reliability and presentation of time. In it indisputable advantage of hourglasses before other types of hours - mechanical, electronic and others.