This section is from the book "Preserving And Pickling", by Mary M. Wright. Also available from Amazon: Preserving and Pickling: Two Hundred Recipes for Preserves, Jellies, Jams, Marmalades, Pickles, Relishes and Other Good Things.
Divide a watermelon in quarters, and trim away the green outside rind, also remove all the red inside part. Cut the white part into small pieces, either cubes or strips, and cover with a weak brine and let stand overnight. Drain and rinse, and boil in water until the rind is tender enough to be easily pierced with a fork. Make a syrup with water and sugar, allowing one pound of sugar to each pound of melon, also one thinly-sliced lemon to each pound of fruit, and one-half teaspoonful ground ginger root. Boil the syrup until thick, and add the fruit, and simmer slowly until transparent. Fill into jars, pour over syrup and seal.