Hourglass

time · gravity · history

Sand falls down. An hourglass has two glass bulbs stacked on top of each other with a tiny hole between them. Sand in the top bulb slowly flows down through the hole to the bottom bulb because of gravity, and when all the sand reaches the bottom, a set amount of time has passed.

Two matching halves. Most hourglasses have the same shaped bulb on top and bottom, which looks beautiful and balanced. The two bulbs are connected by a narrow neck that controls how fast the sand can flow through.

Different sands, different times. An hourglass measures different lengths of time depending on how much sand is inside and what size the sand grains are. Coarser, bigger sand grains fall faster than fine sand, so makers can adjust both the sand and the hole width to create hourglasses that measure 1 minute, 1 hour, or any other duration they want.

Easy to flip. When all the sand reaches the bottom, you simply flip the hourglass upside down and the sand starts falling back the other way. This makes hourglasses super convenient to use over and over again without needing anything else.