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San Francisco's 150 Years of Tidal Observations Obtaining a continuous record of the tides in San Francisco since 1854 has been a testament to human perseverance and ingenuity. To observe the clockwork nature of our universe, we have few backdrops as dramatic as the Golden Gate. Twice each day the tides flood into San Francisco Bay, and twice they rush out on the ebb. Ships plan their sailing and docking times according to these daily risings and fallings. Commercial and naval wharves, seawalls, the great bridges of the Bay Area, underwater communications cables, and pipelines have all been engineered and built taking the tides into consideration. Fishermen, beachcombers and tidepoolers, surfers, and lovers of the shore all are affected by the tides. Although people have observed tidal phenomena for thousands of years, systematic study and prediction of tides are relatively recent. Both Alexander the Great in 325 B.C. and Julius Caesar in 55 B.C., being accustomed to the Mediterranean Sea, which has little tidal variation, almost met disaster because of tidal events. Alexander’s fleet nearly met its end when it was marooned on the Indus River, and Caesar’s boats were so battered by the surges of a high English Channel full-moon tide while closely anchored that his fleet was forced to retreat from a battle with the Britons. For centuries many observers had noted the relationship between phases of the moon and tidal range, and some produced crude tide tables. It was not until 1687, however, that Sir Isaac Newton determined that tides are caused by variable gravitational forces of the sun and moon. The complete version of this article is available at: http://tidesandcurrents.noaa.gov/publications/150_years_of_tides.pdf To return to the article, click here. |