Hourglass. Grains of sand fall from the upper to the lower glass bulb,measuring a fixed length of time. Hour glasses were first used by the Romans in about 1 BC | |
Lizenzart: | Lizenzpflichtig |
Credit: | Science Photo Library / Terry, Sheila |
Bildgröße: | 3801 px × 4615 px |
Modell-Rechte: | nicht erforderlich |
Eigentums-Rechte: | nicht erforderlich |
Restrictions: | - |