• A magnetized iron needle was rubbed with lodestone to create magnetic polarity.
• The needle was placed on a small piece of cork, reed, or bamboo, allowing it to float freely.
• This setup was placed in a bowl of water, reducing friction and stabilizing the movement.
• The needle consistently aligned north–south, giving sailors a reliable reference during voyages.
• This simple device became the earliest form of a marine water compass.

When It Was Used
• First appeared in 11th–12th century China during the Song Dynasty.
• Adopted soon after by Arab navigators through trade routes.
• Reached Europe by the 12th–13th century, widely used by Mediterranean and Atlantic sailors.
• Became the foundation of early long-distance voyages across Asia, the Middle East, and Europe.

Why It Was the First Marine Compass
• It was the first design stable enough to function on a moving ship, even during waves.
• Provided direction when skies were cloudy, foggy, or stormy, when celestial navigation was impossible.
• Allowed sailors to maintain a steady course in open ocean, not just coastal waters.
• Its simplicity made it cheap, easy to build, and highly reliable for early maritime cultures.
• This tool marked the beginning of true open-sea navigation, eventually evolving into the dry compass and modern gyrocompass.