High Altitude Observations of Earth

Before the advent of aviation adventure seekers flew miles high in hot air balloons. These high altitude trips allowed aeronauts to observe the true nature of Earth without peering through the distorted nature of glass, windows, or a fish-eye lens. With the unaided eye they recorded their observations. Here are their testimonies.

“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 skeptical 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 traveler 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.

“It seemed a flat disc with upturned edge”
– Auguste Piccard 1931

“The appearance which the earth presents when seen from a balloon is peculiar, and at a first view suggests anything but the idea of a convex surface such as a globe like the earth might be expected to present. The earth beneath the balloonist appears in fact like a gigantic basin, the rim of which is the horizon all round him, while its deepest part lies below him. Mr. Glaisher (I refer to the eminent meteorologist and aeronaut, not his logarithmic offspring, the Glaisher of Prime Factors, to whom the expansion of logarithms-Characteristic One—is of more interest than that of any balloon the world has yet seen) has spoken of this illusion, though of course he was in no sense deceived by it.*

Fig. 18 illustrates the peculiar effect in question; but I have added to the illusion affecting the aspect of the earth’s surface another, equally marked and much more familiar, affecting the aspect of the clouds.

The explanation of both peculiarities is the same. In my papers on Clouds and their Appearance I have shown how we are deceived into the idea that the clouds form a sort of dome over our heads, whereas the under surface of a layer of clouds, though slightly arched, is in reality very nearly flat within the range of view commanded by the eye. The eye is not sensible of the much greater distance separating us from the clouds near the horizon than from those overhead; and losing the effect of distance we picture the cloud-surface near the horizon as springing almost if not quite vertically from the earth’s surface, to arch over, gradually at first and more rapidly afterwards, towards the point overhead. When we view the under surface of clouds from a balloon situated as shown in Fig. 18, a similar effect is produced.

But also, and for precisely similar reasons, a similar effect is produced on the appearance of the earth’s surface below us. When we look directly down we see that the earth lies far below us, the greatness of the distance being very obvious and striking. On the other hand when we look towards the horizon, although the line of sight really is depressed slightly below the horizontal direction, the depression is not at all obvious, even when we are a mile or two above the sea-level.

Say for instance we are even so much as two miles above the sea-level.
Then from what has been already shown, the depression of the visual horizon (suppose it to be a sea horizon) below the true horizontal direction, corresponds to the angle subtended by four miles at the distance where the line of sight from a height of 2 miles touches the sea level.

This distance, neglecting refraction, which really increases it,* is represented in miles by sqrt(2×8000) or √16000, or by about 127 miles subtends less than 2 degrees, which to the eye appears but an insignificant angle.
Comparing unconsciously this slight depression of the horizon, with the obvious and startling depression of the earth’s surface underneath his car, the aeronaut is deceived into the impression that the surface underneath rises up all around him to his own level or nearly so,—in other words the illusion of a basin-shaped depression such as is shown in Fig. 18 is produced.

footnotes: Mr. Glaisher thinks the earth may have a concave surface — so that as the astronomer holds the earth to be convex while the aeronaut thus misrepresented-holds it to be concave.”

-Pretty Proofs of the Earth’s Rotundity by Richard A. Proctor (KNOWLEDGE – An Illustrated Magazine of Science Volume IV) [July to December 1883]

https://books.google.com/books?id=gLY_AQAAMAAJ&pg=PA275&dq=%22aeronaut%22+concave&hl=en&newbks=1&newbks_redir=0&sa=X&ved=2ahUKEwiYoI3A9O-CAxUyBDQIHbXPBUYQ6AF6BAgtEAI#v=onepage&q=%22aeronaut%22%20concave&f=false

APPEARANCE OF THE EARTH VIEWED FROM A BALLOON.

All perception of comparative altitudes of objects on or near the ground is lost-houses, trees, the undulation of the country, &c., all are reduced to one level, and even the lower detached clouds appear to rest on the earth; everything, in fact, seems to be on the same level, and the whole has the appearance of a plane.
Everything seen, looking downwards from a balloon, including the clouds, seems projected upon the one visible plane beneath. Always, however great the height of the balloon, when I have seen the horizon it has roughly appeared to be on the level of the car-though of course the dip of the horizon is a very appreciable quantity-or the same height as the eye. From this one might infer that, could the earth be seen without a cloud or anything to obscure it, as that point of the plane beneath is directly under the eye, and the boundary line of the plane approximately the same height as the eye, the general appearance would be that of a slight concavity; but I have never seen any part of the surface of the earth other than as a plane. Towns and cities, when viewed from the balloon, are like models in motion. I shall always remember the ascent of the 9th October, 1863, when we passed over London about sunset. At the time when we were 7,000 feet high, and directly over London Bridge, the scene around was one that cannot probably be equalled in the world.”

-James Glaisher, Travels in the Air, (page 99) 1871
https://archive.org/details/Travelsair00Glai/page/98/mode/2up?q=concavity