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

1-8
: 1s & 4s petronella turn into centre & all set in diamond formations,
  1s+2s & 3s+4s dance RH across once round
9-16
: 1s+4s dance 1/2 reel of 4 up/down middle; pass partner by RSh, turn to
  the right & turn person on right RH (1M+3L, 1L+3M, 4M+2L & 4L+2M) to
  end BtoB between 3s/2s
17-24
: 4s+2s & 1s+3s dance reels of 4 across, 1s & 4s end turning RH to form
  line up/down centre with Ladies in centre LH joined
25-32
: 4s+1s Bal-in-Line, turn ptnr 3/4 RH, dance out to ends, turn & face
  2s/3s who have danced in (2s face up & 3s down), 4s+2s also 3s+1s set
33-36
: 4s+2s & 3s+1s dance a Half Rondel :

: 4s/3s dance down under the arch made by 2s/1s who dance up, Ladies cross
  in front of Men & all cast to meet the other Lady or Man on the
  opposite side
37-40
: All join nearer hands on sides, set & cross RH back to own sides. End 2
  4 (1) (3)