Further correspondence between John Nye and James Callahan discussing algebreic geometry and water drops under gravity Additional correspondence between Callahan and Nye, following the publication of Nye's paper in 1979 ['Optical caustics from liquid drops under gravity' published in Philosophical Transactions A]. Includes a set of E6 clock diagrams sent to Nye by Callahan, and later correspondence regarding work by Nye on the X9 singularity. Includes some manuscript notes made by Nye when Callahan came to visit him in Bristol in 1981. 1979-1985