Peel the melon and remove the centre pith, reserving the pips. Cut the flesh into cubes. Wash the lemons, wipe dry and peel with a vegetable peeler to remove only the yellow rind. Cut the fruit in halves and squeeze out the juice. Strain off the juice into a small bowl. Put the lemon peel (yellow part only) and the pips and pulp from the squeezer and the pips from the melon into a loose muslin bag and add this to the melon in the preserving-pan. Heat gently until the juice runs and then cook gently until the melon is tender and transparent (30–45 min.). Remove the muslin bag. Add the lemon juice and sugar and stir without further heating until the sugar is completely dissolved. Bring to the boil and boil as rapidly as possible until a set is obtained. Pour into hot, dry jars and cover.