"Upon his return to Germany and having been appointed as Director of the Deutsche Seewarte, Neumayer conceived and implemented the drift bottle experiment that

"Upon his return to Germany and having been appointed as Director of the Deutsche Seewarte, Neumayer conceived and implemented the drift bottle experiment that would last from 1864 to 1933, and include thousands of bottles. Of all these jettisoned bottles only an estimated 8-10% (662 message slips) found their way back to Hamburg" 10% is not bad really. Also, it gives you a rough estimate of the chance of your 'rescue' message ever reaching anyone.