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 | |
Licence : | Droits gérés |
Crédit: | Science Photo Library / Tek Image |
Taille de l’image : | 3673 px × 4770 px |
Model Release : | Non requis |
Property Release : | Non requis |
Restrictions : | - |