Drift bottle for studying ocean surface currents, issued by the Ministry for Agriculture and Fisheries, London, UK, 1919-1955. Enclosed paper with instructions: ‘BREAK THE BOTTLE | CASSEZ LA BOUTEILLE | BREK DE FLESCH | BRESCHEN DIE FLASCHE | SLAA FLASKEN ITU.’ Obscured instructions direct the finder to make contact with the Ministry.

For thousands of years, people have used the movements of objects floating on the surface of the ocean as a way of understanding ocean currents. Bottles like this were adopted by scientists in the 1800s, who would release them into the sea in known locations. They carried a message inside encouraging anyone who found them to break the glass, so that information could be reported back to the researchers.