The idea is that Jupiter's tides are 33 % higher at perihelion, hence the 1 / J, and if Saturn happens to be in conjunction [every 19.86
years] with Jupiter at that
time the tides are even higher [a «
spring tide» if you want], and because
times are raised on both sides
of the Sun, it will also happen if Saturn is on the
other side
of the Sun
than Jupiter, hence every 19.86 / 2 = 9.93
years, so that is how the 60 - yr period comes about: 61 yr = 1 / (1/9.93 — 1/11.86).