Knight's Mechanical Encyclopedia, S., Sand-glass.

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19th-Century American

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Sand-glass.

A time-measurer, consisting of a vessel containing a measured amount of sand, which is allowed to escape through a hole of definite proportions so as to occupy a certain time in so doing.

The sand-glass was derived from or suggested the clepsydra, or water-clock, in which the lapse of time was indicated by the escape of water from a hole in a vessel. This was probably the first time-measurer acting mechanically. Previous to this the lapse of time was counted by the dial, by devices such as the counting of pebbles from one helmet to another by the Franks and Norsemen; a measured tread and counted paces; the time required to recite the prayers, as indicated by the beads. See clepsydra.

The clepsydra assumed various forms.

1. In one case a brass dish with a hole in the bottom was floated in a cistern, and the time required for its filling and submergence formed a unit of time.

2. The emptying of a large brazen vessel, the side of which was pierced with a small hole.

3. A vessel similar to the foregoing, with a float and graduated stem, indicating time by its subsidence.

4. The device No. 3, with the addition of a string from the float, to turn an axis and a pointer finger on a figured dial.

5. A clepsydra in which the escaping water turned a wheel which communicated motion to a hand on a dial. See clepsydra.

These devices were subject to many difficulties such as the evaporation of the water, which affected those depending upon the measured amount, and the unequal rate of flow at different stages of fullness of the discharging-vessel.

At what period toothed gearing was invented cannot be readily ascertained. Archimedes used it 220 B. C., and probably saw it in Egypt.

Sand, as the flowing material, is stated by some authorities to have been introduced in France about the time of Charlemagne, but this is an error.

On an ancient bas-relief in Rome an hour glass is placed in the hands of Morpheus. Athenaeus says that the ancients carried portable hour-glasses with them.

The term translated hour-glass does not warrant the idea that glass was used. The probable material was horn, or the mineral then so much used for windows, laminated mica, the lapis specularis of Pliny. The two chambers were probably separated by a plate having a drilled opening. See hour-glass.

It may be mentioned in this connection that the first dial on record is that of Ahaz, 742 B. C. It was probably derived from Assyria. See dial.

The dial is mentioned in the book of Tobit. The date of the writing of this book is not certain, but it details the experiences of an Israelite of Naphtali, a prisoner in Nineveh in the reigns of Shalmanezer and Sennacherib.

The statement of Herodotus that the Greeks derived the sundial from the Chaldeans is no doubt correct. In the time of [2026] Ahaz, the communications between Assyria and Palestine were open and well traveled, as the Israelites well knew and felt.

Homer describes the sun-dial, 950 B. C.

The dial was introduced in Athens by Meton, 433 B. C.

By L. Papirius Cursor into Rome, 293 B. C.

Hipparchus used a dial at Alexandria, 130 B. C.

Augustus set one up on a magnificent scale in the Campus Martius. See dial.

1877.

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Knight's Mechanical Encyclopedia
Knight, Ed.

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Sand-glass.

Knight's Mechanical Encyclopedia Knight, Ed.

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Sand-glass.

Knight's Mechanical Encyclopedia
Knight, Ed.