Auguste Picard Reports Earth View as Disk from 9.9 miles up (51,775 ft)!
"Through portholes the observers saw the earth through coper colored then bluish, haze. It seemed a flat disk with upturned edge." (“Ten Miles High in an Air-Tight Ball.” Popular Science Magazine, pg 23 Aug. 1931).
Interestingly, Piccard remarked in an interview shortly after this journey that the world seemed a strange place to although he'd only been off it 18 hrs. ("Two Almost Die in Balloon’s Cage.” Chicago Daily Tribune, pg 1. May 29. 1931.)