[47] Rays flowing from the Sun seem to be red orange or yellow, according to the Quantity of Vapours floating in the Atmosphere, which absorbs the most refrangible ones: and the fewer the Vapours the more does the Sun’s Light approach to a perfect and intense white, according to the Doctrine of Newton: which seems to receive Confirmation from the Purity of the Solar Light, when seen above Clouds and Vapours, in the Balloon: where the Sun shines not so much with a golden as with a sparkling silver Light.
[48] Sounds immediately under the Balloon, seemed, as if originated near the Ear, and louder than they would have been heard, at the Distance of some Yards only, when on a Level with themselves: augmenting rather than decreasing, during the Ascent of the Balloon, till it arrived to a Height indicated by the Barometer at 27 Inches. Presently afterwards, the Balloon still rising; the Sounds died away: much sooner indeed than was expected.
The like was observed in descending from a State of perfect Tranquillity and Silence: Sounds from below, when about the same Height, suddenly rushing on the Ear.
It must be considered that by this Time, the shadows were much encreased; tho’ at half past II, they were more than double in Length to the Height of each Object.
The Trees woud therefore spread a shade across the Road.
The tops of the Houses likewise, being Part of them in the Shade; and either thatched with Straw, or covered with Slates of a dusky Hue; woud prevent their throwing off any striking Colour.
Possibly the Encrease of Shade alone, might give the Face of the Country below, a dark-green Cast.
It is certain that the Height of the Balloon must have been very great, to prevent the Sight of public and Turnpike-Roads, above which it frequently passed, and which had been plainly seen before the Re-ascent.
For suppose the Road but 5 Yards wide, which is less than the Truth; if it be allowed that an Object may be distinguished by a sharp-sighted Person, when its Distance from the Eye does not exceed 5156 Times the Diameter of the Object; i. e. when the Object does not subtend a less Angle at the Eye than 30 Seconds of a Circle, (Smith’s Optics, Article 97) which is the smallest visible Point, and equal to the 8000th Part of an Inch on the Retina;—by multiplying 5 Yards, viz. the Diameter of the public Road, into 5156 (or, in round Numbers, into 5000) Times its Distance from the Eye in the Balloon; the Product is 25000 Yards: which Product being divided by 1760, the Number of Yards in a Mile, amounts to 14 Miles, and 360 Yards.
Supposing farther, that a common Eye can only see an Object at half that Distance; the Height woud then be 7 Miles.