An hourglass (or sandglass, sand timer, or sand clock) is a device used to measure the passage of time. It comprises two glass bulbs connected vertically by a narrow neck that … See more

While some early hourglasses actually did use silica sand as the granular material to measure time, many did not use sand at all. The material used in most bulbs was "powdered See more

Unlike most other methods of measuring time, the hourglass concretely represents the present as being between the past and the See more

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Little written evidence exists to explain why its external form is the shape that it is. The glass bulbs used, however, have changed in style and … See more

Hourglasses were an early dependable and accurate measure of time. The rate of flow of the sand is independent of the depth in the upper … See more

Because of its symmetry, graphic signs resembling an hourglass are seen in the art of cultures which never encountered such objects. Vertical pairs of triangles joined at the apex … See more