Hour glass. Grains of sand falling in an hour glass. An hour glass is an ancient instrument used to measure a fixed length of time by allowing a fixed quantity of sand to flow through a hole. Small hour glasses are known as egg- timers. This is because they have been found useful in measuring the time necessary to boil an egg | |
Lizenzart: | Lizenzpflichtig |
Credit: | Science Photo Library / Tek Image |
Bildgröße: | 3673 px × 4770 px |
Modell-Rechte: | nicht erforderlich |
Eigentums-Rechte: | nicht erforderlich |
Restrictions: | - |