Grapefruit and Melon Jelly

Peel the grapefruit, removing the skin and pith completely. Cut the flesh from the membranes, working over a bowl to catch the juices. Chop the grapefruit and honedew flesh and combine in a bowl with sugar and lemon juice for 1 hour. Soften the gelatin sheets in cold water. Strain the grapefruit-melon mixture through a sieve, catching the juice. Add enough additional grapefruit juice to make 500 ml (about 4 cups). Squeeze the gelatin dry and transfer to a small bowl over simmering water. Stir unil dissolved and stir in a little of the grapefruit-melon juice. Stir the gelatin mixture into the rest of the strained grapefruit-melon mixutre. Sweeten to taste if necessary or desired.