Map and letter from US Navy to Donald MacKinnon, Brock, about `Bottle Paper Drifts`, dated 1929.
Map of the Atlantic showing the direction and frequency of ocean currents from data collected from `Bottle Papers` thrown overboard by the US Navy during 1924-1929, and a letter from the Hydrographic Office of the US Navy to Donald MacKinnon, Ruaig, in 1929, thanking him for the returned bottle paper that he found on Tiree.