The postcard was addressed to George Parker Bidder III – a significant figure in the development of the MBA. Bidder released over 1,000 ‘bottom trailer’ bottles into the North Sea between 1904 and 1906 in what could be described today as a ‘citizen science’ project. (Bottom trailer bottles are adjusted to trail a wire to float with the current two feet above the seabed and be caught in trawl nets.)
The most significant find was that many bottom trailers in the southern North Sea got washed onto the English coastline whereas floating bottles mostly moved across the North Sea towards the continent. From this, Bidder deduced that river outflow caused a shoreward flow of denser salt water, according to the MBA.