3. 19th century balloon observations
This is old 19th century anecdotal evidence from the flat earthers’ favourite book Zetetic Astronomy by Samuel Birley Rowbotham. Many balloonists of his day who reached between 1 and 2 miles altitude commented on how the Earth looked like a concave bowl beneath them.
An observer from a hot air balloon looks to be above a bowl when 1 mile high.
“THE APPARENT CONCAVITY OF THE EARTH AS SEEN FROM A BALLOON. – A perfectly-formed circle encompassed the visibly; planisphere beneath, or rather the concavo-sphere it might now be called, for I had attained a height from which the earth assumed a regularly hollowed or concave appearance – an optical illusion which increases as you recede from it. At the greatest elevation I attained, which was about a mile-and-a-half, the appearance of the world around me assumed a shape or form like that which is made by placing two watch glasses together by their edges, the balloon apparently in the central cavity all the time of its flight at that elevation.” – Wise’s Aëronautics.
“Another curious effect of the aërial ascent was that the earth, when we were at our greatest altitude, positively appeared concave, looking like a huge dark bowl, rather than the convex sphere such as we naturally expect to see it… The horizon always appears to be on a level with our eye, and seems to rise as we rise, until at length the elevation of the circular boundary line of the sight becomes so marked that the earth assumes the anomalous appearance as we have said of a concave rather than a convex body.” – Mayhew’s Great World of London.
“The chief peculiarity of a view from a balloon at a consider-able elevation, was the altitude of the horizon, which remained practically on a level with the eye, at an elevation of two miles, causing the surface of the earth to appear concave instead of convex, and to recede during the rapid ascent, whilst the horizon and the balloon seemed to be stationary.” – London Journal, July 18th, 1857.
“I don’t know that I ever hinted heretofore that the aëronaut may well be the most sceptical man about the rotundity of the earth. Philosophy imposes the truth upon us; but the view of the earth from the elevation of a balloon is that of an immense terrestrial basin, the deeper part of which is that directly under one’s feet. As we ascend, the earth beneath us seems to recede–actually to sink away – while the horizon gradually and gracefully lifts a diversified slope, stretching away farther and farther to a line that, at the highest elevation, seems to close with the sky. Thus, upon a clear day, the aëronaut feels as if suspended at about an equal distance between the vast blue oceanic concave above and the equally expanded terrestrial basin below.” – Mr. Elliott, an American balloon aëronaut, in a letter giving an account of his ascension from Baltimore.
“The plane of the earth offers another delusion to the traveller in air, to whom it appears as a concave surface, and who surveys the line of the horizon as an unbroken circle, rising up, in relation to the hollow of the concave hemisphere, like the rim of a shallow inverted watch-glass, to the height of the eye of the observer, how high soever he may be–the blue atmosphere above closing over it like the corresponding hemisphere reversed.” – Glaisher’s Report, in “Leisure Hour,” for May 21, 1864.
There are two main questions to this kind of evidence: 1. Where are the modern balloonists’ testimonies? Maybe they also see the same thing but have not found it remarkable enough to comment in a book or on the internet. 2. Passengers on jet airplanes cruising at 10/11 km high do not see the Earth’s concavity, merely its flatness. It could be that the windows alter perception? Or perhaps it is because the observer has such a narrow field of view and cannot see 360° around themselves as a balloonist can?
The standard explanation given for this “bowl” effect is that it is an optical illusion. This could be a definite possibility, although no real supporting evidence has been presented. On the above grounds, I give this evidence for concave Earth at about 30%.