The opposing swirls of the paisleys on my tie help honor the birthday of Gaspard-Gustave de Coriolis in 1792. This French physicist was the first to explain how angular momentum behaves in a rotating frame of reference -- which is most evident to us in the way weather patterns in the Northern Hemisphere rotate clockwise, while those in the Southern Hemisphere rotate counterclockwise. The "Coriolis effect" is observable only for large-scale phenomena like major storms and large cloud formations. Although some popular mythology says that it causes water to drain in opposite swirling directions in the two hemispheres, the forces that actually do produce the Coriolis effect are far too weak to affect the liquids we meet every day. Coriolis is also known as the first person to give the physical description of "work" as a force moving through a distance (in 1829).