Half and one hour double glass

From Object Wiki

Half and one hour double glass
Manufacturer	(unknown)
Production years	(unknown)
Production location	(unknown)

Half- and one-hour double glass. The half-hour glass is probably a replacement.

[edit] How it works

The timekeeping depends on the regular flow of sand through a small orifice. The time taken for one bulb of the sand glass to empty is a definite interval, at the end of which the glass can be turned over and the process repeated. Sand glasses are useful for measuring long periods of time, but prove inadequate for short time intervals.

[edit] Memories

Do you remember stories about sand glasses? Add your memories.

[edit] In the Science Museum's Records

Inv. No: 1953-313