214. It has been already noted, that at a certain Height, a Kind of +chilliness+ was perceived, not ascertainable by the Thermometer. The Sensation was _suddenly_ impressed four Times, in ascending and descending to and from the same Height, viz. about 26 and 27 Inches, equivalent to between 500 and 1000 Yards above the Surface of the Earth at the first Ascent. 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. [Sidenote: 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? [Sidenote: Visibility of Vapours by mere Distance.] And hence the Visibility of Vapours by _mere_ Distance, which contains a sufficient Number of Particles to intercept and refract the Light, without Cold, Condensation, or _actual_ Accumulation: viz. by Refrangibility of those primary Rays of Light, which Air and Vapour united are most _apt_ to reflect or transmit.