The invention of the life preserver during the 19th century was a milestone in public health, mainly because knowing how to swim did not become essential to Americans until the early 20th century. On this date in 1841, N.E. Guerin won a U.S. patent for the first life preserver. His was filled with cork, a lightweight, spongy substance that repels water rather than absorbing it. Today, life jackets are filled with even lighter material, usually kapok, plastic foam or fiberglass, or sometimes are inflated with air. Life preservers are not a modern invention; soldiers inflated animal skins during the ninth century to keep themselves afloat when they crossed streams and other bodies of water.

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