Science Art: Fig 172 – Results of Dr. Fulton’s Drift-Bottle Experiments in the North Sea, 1912.

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This is a map of something invisible – ocean currents – made indirectly – by releasing messages in bottles and seeing where they land, based on who sent back the enclosed slip from where.

Nowadays, indirect observations like this are a little more complicated, but the same basic principles are still at play in things like astronomy, space travel, meteorology, and medicine. If you can’t see it, try to find some way to watch what it does.

This image is from The Depths of the Ocean : A general account of the modern science of oceanography based largely on the scientific researches of the Norwegian steamer Michael Sars in the North Atlantic.

[via nemfrog]