A replica Tempest Prognosticator at the Whitby Museum, Whitby, UK. The tempest prognosticator was a weather forecasting system which attempted to predict storms with leeches trapped inside glass jars. An approaching storm was supposed to cause the leeches to climb chains dangling in the jars. The leeches climbing up the the chains caused bells to ring and warn of an approaching tempest. The device was invented in the 19th-century by George Merryweather.