Alexander Dyce, A General Glossary to Shakespeare's Works

water-galls secondary rainbows, THE RAPE OF LUCRECE, 1588. (This word, far from common even in our early writers, is several times used by Horace Walpole: “False good news are always produced by true good, like the watergall by the rainbow;” again,“Thank heaven it is complete, and did not remain imperfect like a watergall;” again, “But what signifies repeating the faint efforts of an old watergall opposed to its own old sun!” Letters, vol. i. p. 310, and vol. vi. pp. 1, 187, ed. Cunningham. In The Dialect of Craven we find “Weather-gall, A secondary or broken rainbow. Germ. wasser-galle, repercussio Iridis.”)