CHAPTERXXXVIII.ON CERTAIN APPEARANCES AT DIFFERENT ALTITUDES OF THE BALLOON.Of the highest visible Clouds which are alwayswhite.Section 213.THE highest visiblewhiteClouds, often seen in detached Streaks, during the finest and also in the worst Weather, (if not intercepted by lower Clouds) and which, when melting away, are known in some Counties by the common Appellation of Horse-Tails; and, suspended over Great-Britain, are frequentlymarbledor dappled by the Wind; putting on the Appearance of white Waves, like Sea-Sands ruffled and left by a rapid Tide;—had been disturbed, separated, and almostmelteddown by theStormthe Day preceding the Excursion.Two of themonlywere still visible in Streaks, near the Sun’s Place, at the first Ascent. Theyseemed without Motion, and became afterwardsinvisible.Saussure, the celebrated Professor of Philosophy at Geneva, is very exact in his Definition, Description, and Height of these Appearances: and thinks itprobable, their Situation may be “at least fifteen English Miles above the Surface of the Earth.”“Car quand je considere ces fines Pommelures, &c.”“For when I consider these delicate Dapplings, which, in a Series of fair Weather, begin to cover the azure Vault of Heaven with a white and transparent Gauze, and which portend Rain a long Time before it happens; I am led to believe they occupy a very elevated Situation in the Atmosphere” (Essais sur l’Hygrometrie, P. 271.)It seems however thatCrosbie, in his Excursion from Dublin on the 25th of January 1785, pierced throu’ and soared above thesefine Webs, at the Height of 16 Inches by the Barometer in afrostyAir.Of theChillinessperceived at a certain Height.214. It has been already noted, that at a certain Height, a Kind ofchillinesswas perceived, not ascertainable by the Thermometer.The Sensation wassuddenlyimpressed 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 notpass throu’ any visible Cloud or Vapour, during the Excursion. SeeSection 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; thecircularProspects of the subjàcent Earthinstantlycontracted, and, during the Descent, about the same Height,instantlyenlarged themselves to the Eye of the Aironaut.216. At the same Height mentioned before, thecircularProspects of the Clouds appeared on the same horizontal Plane with the Eye: tho’ at the Distance of a Mile. SeeSection 49.InthisSituation, the Observer endeavoured to discover the Thickness of theStratumof Clouds: but was always baffled by a Deception of Sight worth recording.TheStratawere plainly composed of three or more Heights of Clouds,sailingat great Intervals, one above the other: all which regularlyvanished, as he approached their respective Levels: as ifinstantlythrown into the Circumference of a Circle, whose Radius was a Mile.During the Ascent, in passing their supposed Level, the Cloudsinstantlyappearedfar belowhim: and during the Descent, as farabove.217. Quere: Is it not from the same Cause, that all Vapour isgenerallyinvisible to a certain Height and Distance from the Eye?It being incontrovertible that more Vapours rise aboutnoon, than at any other Hour, particularlyat Sea, while the Sun continues toshine; which, notwithstanding, are whollyinvisible, till arrived at acertainHeight?Visibility of Vapours by mere Distance.And hence the Visibility of Vapours bymereDistance, which contains a sufficient Number of Particles to intercept and refract the Light, without Cold, Condensation, oractualAccumulation: viz. by Refrangibility of those primary Rays of Light, which Air and Vapour united are mostaptto reflect or transmit.Mons. Saussure has proved by his Horse-Hair comparàble Hygrometer, that “the Air shews Signs ofgreatestHumidity an Hour after Sunrise, and ofleastHumidity, between three and four in theAfternoon.” But the Air beingthenalso the hottest, willdissolveor evaporate the greatest Quantity of Vapours, and raise themabovethe Hygrometer (which by itsHeatwill not retain, but on the contrary repel anddissipatethem) to great Heights in the Atmosphere.See “Essais sur l’Hygrometrie, C. 6, P. 315.”218. In general then:Is not theCauseof the above Deceptions,notanAbsence, but aTransparency of Vapourto a certain Distance: (just as the Zenithappearscloudless, when the Air isovercastaround;) beyond which Distance, theNumberand relative Proximity of Particles with Respect to the Eye, is such, as to intercept the Rays of Light:when only, they put on theColourof Air, and Form of Vapour and Cloud?And hence the probable Reason, whynocircularHorizon of the Earth’s Surface was presented during the Excursion, Section 79: andwhy it seldom has or can present itself to Aironauts orMountaineers, at anyconsiderableHeight above the Region or Level of Clouds, even tho’ Clouds donotappear in the Air, either to themselves, or to Spectatorsbelow.This Point seems capable of Illustration by Analogy, from the Impossibility of encreasing theMagnitude, and at the same Time,Distinctnessof distant Objects, seen throu’ acommonTelescope; on Account of the Quantity of Vapours between them and the EyeWhichvapoursmay be magnified till the Object appears confused and obscure; and even at last become substituted in the Place of the Object, under the Form of Opacity andCloudiness.219. Thegreaterthe Height of the Balloon, the morecontractedwas the Circle of Vapour below it; and the more limited the Prospect of the Earth’s Surface below the Vapour.220. It seemed probable that the Sun shone asbrighton the Countries around the Observer, as on Objects immediately below him: which Objects coud not have been illuminated by the Sun’s Rays, darting throu’ theapparentandcontractedopeningunder him; as the Rays which shone on the Balloon, fell beyond theOpening,obliquelyon Clouds which caught the Shadow of the Balloon.221. The extremeRarityorTenuityof the Vapours wasevidentfrom theprogressiveCourse of the Balloon, which wasalwaysin the Center of acircularOpening, limiting the lower Prospects; except when the Spectator lost all Sightof the Earth, by dense, watry, intervening Clouds.Novel Situation peculiar to the Balloon, again described.Thisaugustcentral Situation,always changing yet still the same, had the most striking Effect on the Senses and Imagination. Yet, however pleasing the Recollection of thisglorious appearance; howeverstronglyimpressed, accurately described, or richly painted; it must fall infinitely short of the originalsensation. Unity and Sameness were there contrasted withperpetual Variety: Beauty of Colouring; Minuteness, and consummate Arrangement;—withMagnificenceandSplendor:actualImmensity;—withapparentLimitation:—all which weredistinctlyconveyed to the Mind, at thesameInstant, throu’ the Intervention of the Organs of Sight: and, to complete the Scene, was added the Charm ofnovelty.
CHAPTERXXXVIII.
Of the highest visible Clouds which are alwayswhite.
Section 213.THE highest visiblewhiteClouds, often seen in detached Streaks, during the finest and also in the worst Weather, (if not intercepted by lower Clouds) and which, when melting away, are known in some Counties by the common Appellation of Horse-Tails; and, suspended over Great-Britain, are frequentlymarbledor dappled by the Wind; putting on the Appearance of white Waves, like Sea-Sands ruffled and left by a rapid Tide;—had been disturbed, separated, and almostmelteddown by theStormthe Day preceding the Excursion.
Two of themonlywere still visible in Streaks, near the Sun’s Place, at the first Ascent. Theyseemed without Motion, and became afterwardsinvisible.
Saussure, the celebrated Professor of Philosophy at Geneva, is very exact in his Definition, Description, and Height of these Appearances: and thinks itprobable, their Situation may be “at least fifteen English Miles above the Surface of the Earth.”
“Car quand je considere ces fines Pommelures, &c.”“For when I consider these delicate Dapplings, which, in a Series of fair Weather, begin to cover the azure Vault of Heaven with a white and transparent Gauze, and which portend Rain a long Time before it happens; I am led to believe they occupy a very elevated Situation in the Atmosphere” (Essais sur l’Hygrometrie, P. 271.)
It seems however thatCrosbie, in his Excursion from Dublin on the 25th of January 1785, pierced throu’ and soared above thesefine Webs, at the Height of 16 Inches by the Barometer in afrostyAir.
Of theChillinessperceived at a certain Height.
214. It has been already noted, that at a certain Height, a Kind ofchillinesswas perceived, not ascertainable by the Thermometer.
The Sensation wassuddenlyimpressed 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 notpass throu’ any visible Cloud or Vapour, during the Excursion. SeeSection 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; thecircularProspects of the subjàcent Earthinstantlycontracted, and, during the Descent, about the same Height,instantlyenlarged themselves to the Eye of the Aironaut.
216. At the same Height mentioned before, thecircularProspects of the Clouds appeared on the same horizontal Plane with the Eye: tho’ at the Distance of a Mile. SeeSection 49.
InthisSituation, the Observer endeavoured to discover the Thickness of theStratumof Clouds: but was always baffled by a Deception of Sight worth recording.
TheStratawere plainly composed of three or more Heights of Clouds,sailingat great Intervals, one above the other: all which regularlyvanished, as he approached their respective Levels: as ifinstantlythrown into the Circumference of a Circle, whose Radius was a Mile.
During the Ascent, in passing their supposed Level, the Cloudsinstantlyappearedfar belowhim: and during the Descent, as farabove.
217. Quere: Is it not from the same Cause, that all Vapour isgenerallyinvisible to a certain Height and Distance from the Eye?
It being incontrovertible that more Vapours rise aboutnoon, than at any other Hour, particularlyat Sea, while the Sun continues toshine; which, notwithstanding, are whollyinvisible, till arrived at acertainHeight?
Visibility of Vapours by mere Distance.
And hence the Visibility of Vapours bymereDistance, which contains a sufficient Number of Particles to intercept and refract the Light, without Cold, Condensation, oractualAccumulation: viz. by Refrangibility of those primary Rays of Light, which Air and Vapour united are mostaptto reflect or transmit.
Mons. Saussure has proved by his Horse-Hair comparàble Hygrometer, that “the Air shews Signs ofgreatestHumidity an Hour after Sunrise, and ofleastHumidity, between three and four in theAfternoon.” But the Air beingthenalso the hottest, willdissolveor evaporate the greatest Quantity of Vapours, and raise themabovethe Hygrometer (which by itsHeatwill not retain, but on the contrary repel anddissipatethem) to great Heights in the Atmosphere.
See “Essais sur l’Hygrometrie, C. 6, P. 315.”
218. In general then:
Is not theCauseof the above Deceptions,notanAbsence, but aTransparency of Vapourto a certain Distance: (just as the Zenithappearscloudless, when the Air isovercastaround;) beyond which Distance, theNumberand relative Proximity of Particles with Respect to the Eye, is such, as to intercept the Rays of Light:when only, they put on theColourof Air, and Form of Vapour and Cloud?
And hence the probable Reason, whynocircularHorizon of the Earth’s Surface was presented during the Excursion, Section 79: andwhy it seldom has or can present itself to Aironauts orMountaineers, at anyconsiderableHeight above the Region or Level of Clouds, even tho’ Clouds donotappear in the Air, either to themselves, or to Spectatorsbelow.
This Point seems capable of Illustration by Analogy, from the Impossibility of encreasing theMagnitude, and at the same Time,Distinctnessof distant Objects, seen throu’ acommonTelescope; on Account of the Quantity of Vapours between them and the EyeWhichvapoursmay be magnified till the Object appears confused and obscure; and even at last become substituted in the Place of the Object, under the Form of Opacity andCloudiness.
219. Thegreaterthe Height of the Balloon, the morecontractedwas the Circle of Vapour below it; and the more limited the Prospect of the Earth’s Surface below the Vapour.
220. It seemed probable that the Sun shone asbrighton the Countries around the Observer, as on Objects immediately below him: which Objects coud not have been illuminated by the Sun’s Rays, darting throu’ theapparentandcontractedopeningunder him; as the Rays which shone on the Balloon, fell beyond theOpening,obliquelyon Clouds which caught the Shadow of the Balloon.
221. The extremeRarityorTenuityof the Vapours wasevidentfrom theprogressiveCourse of the Balloon, which wasalwaysin the Center of acircularOpening, limiting the lower Prospects; except when the Spectator lost all Sightof the Earth, by dense, watry, intervening Clouds.
Novel Situation peculiar to the Balloon, again described.
Thisaugustcentral Situation,always changing yet still the same, had the most striking Effect on the Senses and Imagination. Yet, however pleasing the Recollection of thisglorious appearance; howeverstronglyimpressed, accurately described, or richly painted; it must fall infinitely short of the originalsensation. Unity and Sameness were there contrasted withperpetual Variety: Beauty of Colouring; Minuteness, and consummate Arrangement;—withMagnificenceandSplendor:actualImmensity;—withapparentLimitation:—all which weredistinctlyconveyed to the Mind, at thesameInstant, throu’ the Intervention of the Organs of Sight: and, to complete the Scene, was added the Charm ofnovelty.