  Because of the lack of reliable sunspot observation, the quality of sunspot
number series is poor in the late 18th century, leading to the abnormally long
solar cycle (1784--1799) before the Dalton minimum. Using the newly recovered
solar drawings by the 18--19th century observers Staudacher and Hamilton, we
construct the solar butterfly diagram, i.e. the latitudinal distribution of
sunspots in the 1790's. The sudden, systematic occurrence of sunspots at high
solar latitudes in 1793--1796 unambiguously shows that a new cycle started in
1793, which was lost in traditional Wolf's sunspot series. This finally
confirms the existence of the lost cycle that has been proposed earlier, thus
resolving an old mystery. This letter brings the attention of the scientific
community to the need of revising the sunspot series in the 18th century. The
presence of a new short, asymmetric cycle implies changes and constraints to
sunspot cycle statistics, solar activity predictions, solar dynamo theories as
well as for solar-terrestrial relations.
