Brief description

A device used to measure the passage of a determined period of time. It comprises two glass bulbs connected vertically by a narrow neck that allows a regulated flow of material (usually sand) from the upper bulb to the lower one.

Use / Function

• Timer: Measuring short, fixed intervals (cooking, games, sermons, watches on ships).
• Durability: Works on ships where pendulum clocks fail due to motion.
• Symbolism: Representation of time running out.

Operating principle

Gravity pulls the granular material through the narrow neck. Unlike water, dry sand (or similar material) flows at a constant rate regardless of the height of the column in the upper bulb, provided the neck is narrow enough and the grains are uniform.

How to create it

1. Bulbs: Blow two glass bulbs or use two separate bottles joined at the necks.
2. Neck: Ensure a smooth, narrow passage. A metal plate with a precise hole can be placed between the bulbs to regulate flow.
3. Fill: Use fine, dry, uniform sand, powdered eggshells, or marble dust. Sift carefully to remove large particles.
4. Seal: Hermetically seal the connection to prevent moisture from entering (which clumps the sand).
5. Frame: Mount in a protective wooden or metal frame.

Materials needed

• Essential: Glass for visibility and smoothness.
• Flow Material: Sand (washed and dried), pulverized eggshells, or metal oxides.
• Structure: Wood or Metal for the stand.

Variants and improvements

• Multiple Glasses: Several hourglasses mounted together for different intervals (e.g., 15, 30, 60 minutes).
• Rotatable Mount: Easy turning mechanism on a wall or stand.

Limits and risks

• Fixed Interval: Can only measure the specific time it was designed for.
• Clogging: Moisture or irregular grains can stop the flow.
• Breakage: Glass is fragile.
• Wear: Sand can erode the neck over time, changing the flow rate (widening the hole).

Related Inventions

• Timepieces
• Water Clock