{{explanation}}
3s & 4s start on opp sides

1-8
: All set, 1s+2s also 3s+4s dance 1/2 double Fig of 8 (1s & 4s crossing
  down/up to start), 1s & 4s turn 2H
9-16
: 1s & 4s dance 1/2 Figs of 8 on sides (out between 2s+3s) & loop round to
  face 2s/3s in lines across, all set & turn 2H
17-24
: 1s & 4s dance 1/2 reel of 4 across with 2s/3s, all set, 1s & 4s
  petronella turn into centre **while** 2s & 3s set
25-32
: 1s+2s also 3s+4s circle 4H round to left, 1s & 4s advance towards
  partner & dance out ends & cast to 2nd/3rd places to end 2 4 (1)(3)