The hypothetical new interaction could be what he and his colleagues call the flavour force—a fifth fundamental force of nature besides gravity and the three of the Standard Model.
Therefore, no single event has more puzzled historians than the sudden, unexplained appearance of at least two new natural forces of the highest educational value in mechanics, for the first time within record of history.
Perhaps the earliest known of all natural forces after the solar energies, it seemed to have suggested no idea to any one until some mariner bethought himself that it might serve for a pointer.