  In addition to the regular Schwabe cycles of approximately 11 y, "prolonged
solar activity minima" have been identified through the direct observation of
sunspots and aurorae, as well as proxy data of cosmogenic isotopes. Some of
these minima have been regarded as grand solar minima, which are arguably
associated with the special state of the solar dynamo and have attracted
significant scientific interest. In this paper, we review how these prolonged
solar activity minima have been identified. In particular, we focus on the
Dalton Minimum, which is named after John Dalton. We review Dalton's scientific
achievements, particularly in geophysics. Special emphasis is placed on his
lifelong observations of auroral displays over approximately five decades in
Great Britain. Dalton's observations for the auroral frequency allowed him to
notice the scarcity of auroral displays in the early 19th century. We analyze
temporal variations in the annual frequency of such displays from a modern
perspective. The contemporary geomagnetic positions of Dalton's observational
site make his dataset extremely valuable because his site is located in the
sub-auroral zone and is relatively sensitive to minor enhancements in solar
eruptions and solar wind streams. His data indicate clear solar cycles in the
early 19th century and their significant depression from 1798 to 1824.
Additionally, his data reveal a significant spike in auroral frequency in 1797,
which chronologically coincides with the "lost cycle" that is believed to have
occurred at the end of Solar Cycle 4. Therefore, John Dalton's achievements can
still benefit modern science and help us improve our understanding of the
Dalton Minimum.

Solar and Stellar Astrophysics;History and Philosophy of Physics;Space Physics