From the Uniformity of Effect at the same Height; the Sensation may be ascribed to the same Cause, viz. the Level of the first or lower Tier of Clouds: altho’ the Aironaut did not pass throu’ any visible Cloud or Vapour, during the Excursion. See [Section 93].
Remarkable Appearances of Earth and Clouds.
215. At the same Height likewise, tho’ the Observations have not been set down at large; the Appearances of the Earth and Clouds were very remarkable.
During the Ascent of the Balloon, between the Altitudes of 26 and 27 Inches; the circular Prospects of the subjàcent Earth instantly contracted, and, during the Descent, about the same Height, instantly enlarged themselves to the Eye of the Aironaut.
216. At the same Height mentioned before, the circular Prospects of the Clouds appeared on the same horizontal Plane with the Eye: tho’ at the Distance of a Mile. See [Section 49].
In this Situation, the Observer endeavoured to discover the Thickness of the Stratum of Clouds: but was always baffled by a Deception of Sight worth recording.
The Strata were plainly composed of three or more Heights of Clouds, sailing at great Intervals, one above the other: all which regularly vanished, as he approached their respective Levels: as if instantly thrown into the Circumference of a Circle, whose Radius was a Mile.
During the Ascent, in passing their supposed Level, the Clouds instantly appeared far below him: and during the Descent, as far above.
217. Quere: Is it not from the same Cause, that all Vapour is generally invisible to a certain Height and Distance from the Eye?
It being incontrovertible that more Vapours rise about noon, than at any other Hour, particularly at Sea, while the Sun continues to shine; which, notwithstanding, are wholly invisible, till arrived at a certain Height?