CHAPTERLI.Section 275.IF then this Reasoning be allowed; aërial Travellers will not be subject, when, at a considerable Height, even in Winter, to great Degrees of Cold, supposing that the Air does not actually freeze the Waters below; and the Apogay or Southerly Winds have continued for a few Days.On the Contrary; Aironauts may expect Cold, encreasing with their Ascent, even in Summer, tho’warmbelow; supposing the Eknèfiai or Northerly Winds to have continued but for a Day before the Ascent: they may possibly, indeed by soaring higher, rise into the regular Stratum of the warm Apogay floating above them.276. From what has been said, there seems a Degree of Probability, that the Air for a Number of Miles,above warm cultivated Plainsshoud differ materially in its Temperature, from Air above Mountains, oreven on a Levelwith their Summits.That the former Air, in moderate Weather, shoud continuewarm and rarefied: while the latter iscool and condensed.For the same Reason the Air over the Sea, on the Hours of Accumulation; i. e. during the Night, in Summer, and frequently in Winter,shoud be foundwarmandrarefied: especially during a Continuance of the Apogay Winds.277. It is likewise probable that the Atmosphere will be foundrespirableat much greater Heights, than is at present imagined: during the Continuance of the Eknèfiai Winds; and also, on Account of thedefloguisticatedAir,[83]which isdrierandless elasticin Proportion to its Rarity.[84]278. The Height of 10 Miles seems not too great to limit human Respiration, shoud any Attempt be made, to soar with a Balloon in a mild Atmosphere; and particularly between the Tropics.[85]But an Objection woud be found in the Size of a Balloon sufficiently capacious to contain nearly 6 Times the Bulk to which the Gass woud necessarily expand itself, at the Height of 10 Miles.First Cause of Limitation, in the Ascent of Balloons.Second Cause of Limitation in the Ascent of Balloons.279. It seems most likely that the primary Cause that will affect the Ascent of Balloons is the Difficulty of encreasing the Dimension of the Balloon: the Second, is from the excessive Cold; if the Wind blows from any Points of the North.Supposing the Construction of the Atmosphere to be as represented by different Authors, (which, by the Way, is scarcely credible) ten Miles will perhaps be the utmost attainable Height.280. There is a Circumstance relative to the Motion of the Air, which has not been sufficiently attended to: and bears some Analogy with that of aThorough Air.This Circumstance may not improperly be called theReceptionandDispersion of Air.In cold Climates, it is an Object of Dread: in warm ones, a most desirable Piece of Luxury.A gentle Undulation of the Air is perceived in Peru, and other hot Climates, by Persons sitting inArbourssheltered from the Sun.The surrounding Air is instantlycontractedbyCondensation, during the Absence of the Sun’s Rays, and therefore occupies aless Space:fresh Airisreceived, and as instantlydispersedby Expansion towards those Parts, which are the warmest, i. e. where there is least Resistance: so that a gentleBreeze is constantly kept up,probablyby a Depression fromabove.[86]281. Analagous to this, are those Winds which generallyrise earlyand die away atSunset: the nocturnal Condensation of the Air being sufficient for thereception: as Air suffers some Compression without Tumult.To demonstrate the Changes owing also to remote and invisible Causes least suspected; Boyle somewhere speaks of an Instrument he made, which was so nicely contrived, that he coud tell, while sitting in his own Apartment, whenever any detached Cloud passed beneath the Sun’s Disk. The Principle on which it acted seems to have been that of a Reception and Dispersion of Air that took Place withintheshadowproceeding from the Cloud.282. An oblique Argument supporting the Doctrine of Depression, asserted to take Place, in fair Weather, is thatWinddrys up the Moisture from the Ground more than theSun: and that March which is thewindiest, is also themost drying, tho’notthehottestMonth.Bacon, in his Enquiry into Motions and Undulations of the Air, uses a Metaphor, which tho’ somewhat facetious, is strictly philosophical.[87]“For whenwindsleadthe dance,it woud be agreeable to know thefigure.”[88]And it is probable, that they really press the Earth with a saltatory progressive undulating Motion,descendingin elastic Steps of sudden Compression; andrisingwith quick alternate ones, of Dilatation and Expansion.Dicker’s Balloon gave Proof of this.283. Lastly: thechillof Airwhich always takes Place overwater, andmoistGrounds, even in thefinest weather, strongly favours theReceptionandDispersionofit, to the surrounding and more heated Lands: (which can only be supplied, as before mentioned, by Torrents of fresh Airgradually descendingfrom the etherial or middle Region of the Atmosphere;) and seems to produce the same Effect, viz. a constant Breeze, with that of the Arbor, Shade, or Shelter from theSun: also with that of theShadowfrom the Cloud passing under his Disk, which affected a complete Thermometer and Hygrometer.284. On a Change of Weather from Frost to Thaw, the Colour of theupper Airfirstalters from aclear and deep, to adull and faintBlue, or to a muddy Haze, not distinguishable into Clouds, but visible above them; a vivid Brightness still remaining, for many Hours, to about 500 Yards above the Surface of the Earth.Or, softwarmShowers fall gently, without Wind, or any apparent Change in its Direction.All which seem to favour the Accumulation and Descent ofwarm Air, by Waves of the Apogay rolling over the Eknèfiai Winds.
CHAPTERLI.
Section 275.IF then this Reasoning be allowed; aërial Travellers will not be subject, when, at a considerable Height, even in Winter, to great Degrees of Cold, supposing that the Air does not actually freeze the Waters below; and the Apogay or Southerly Winds have continued for a few Days.
On the Contrary; Aironauts may expect Cold, encreasing with their Ascent, even in Summer, tho’warmbelow; supposing the Eknèfiai or Northerly Winds to have continued but for a Day before the Ascent: they may possibly, indeed by soaring higher, rise into the regular Stratum of the warm Apogay floating above them.
276. From what has been said, there seems a Degree of Probability, that the Air for a Number of Miles,above warm cultivated Plainsshoud differ materially in its Temperature, from Air above Mountains, oreven on a Levelwith their Summits.
That the former Air, in moderate Weather, shoud continuewarm and rarefied: while the latter iscool and condensed.
For the same Reason the Air over the Sea, on the Hours of Accumulation; i. e. during the Night, in Summer, and frequently in Winter,shoud be foundwarmandrarefied: especially during a Continuance of the Apogay Winds.
277. It is likewise probable that the Atmosphere will be foundrespirableat much greater Heights, than is at present imagined: during the Continuance of the Eknèfiai Winds; and also, on Account of thedefloguisticatedAir,[83]which isdrierandless elasticin Proportion to its Rarity.[84]
278. The Height of 10 Miles seems not too great to limit human Respiration, shoud any Attempt be made, to soar with a Balloon in a mild Atmosphere; and particularly between the Tropics.[85]
But an Objection woud be found in the Size of a Balloon sufficiently capacious to contain nearly 6 Times the Bulk to which the Gass woud necessarily expand itself, at the Height of 10 Miles.
First Cause of Limitation, in the Ascent of Balloons.
Second Cause of Limitation in the Ascent of Balloons.
279. It seems most likely that the primary Cause that will affect the Ascent of Balloons is the Difficulty of encreasing the Dimension of the Balloon: the Second, is from the excessive Cold; if the Wind blows from any Points of the North.
Supposing the Construction of the Atmosphere to be as represented by different Authors, (which, by the Way, is scarcely credible) ten Miles will perhaps be the utmost attainable Height.
280. There is a Circumstance relative to the Motion of the Air, which has not been sufficiently attended to: and bears some Analogy with that of aThorough Air.
This Circumstance may not improperly be called theReceptionandDispersion of Air.
In cold Climates, it is an Object of Dread: in warm ones, a most desirable Piece of Luxury.
A gentle Undulation of the Air is perceived in Peru, and other hot Climates, by Persons sitting inArbourssheltered from the Sun.
The surrounding Air is instantlycontractedbyCondensation, during the Absence of the Sun’s Rays, and therefore occupies aless Space:fresh Airisreceived, and as instantlydispersedby Expansion towards those Parts, which are the warmest, i. e. where there is least Resistance: so that a gentleBreeze is constantly kept up,probablyby a Depression fromabove.[86]
281. Analagous to this, are those Winds which generallyrise earlyand die away atSunset: the nocturnal Condensation of the Air being sufficient for thereception: as Air suffers some Compression without Tumult.
To demonstrate the Changes owing also to remote and invisible Causes least suspected; Boyle somewhere speaks of an Instrument he made, which was so nicely contrived, that he coud tell, while sitting in his own Apartment, whenever any detached Cloud passed beneath the Sun’s Disk. The Principle on which it acted seems to have been that of a Reception and Dispersion of Air that took Place withintheshadowproceeding from the Cloud.
282. An oblique Argument supporting the Doctrine of Depression, asserted to take Place, in fair Weather, is thatWinddrys up the Moisture from the Ground more than theSun: and that March which is thewindiest, is also themost drying, tho’notthehottestMonth.
Bacon, in his Enquiry into Motions and Undulations of the Air, uses a Metaphor, which tho’ somewhat facetious, is strictly philosophical.[87]“For whenwindsleadthe dance,it woud be agreeable to know thefigure.”[88]
And it is probable, that they really press the Earth with a saltatory progressive undulating Motion,descendingin elastic Steps of sudden Compression; andrisingwith quick alternate ones, of Dilatation and Expansion.
Dicker’s Balloon gave Proof of this.
283. Lastly: thechillof Airwhich always takes Place overwater, andmoistGrounds, even in thefinest weather, strongly favours theReceptionandDispersionofit, to the surrounding and more heated Lands: (which can only be supplied, as before mentioned, by Torrents of fresh Airgradually descendingfrom the etherial or middle Region of the Atmosphere;) and seems to produce the same Effect, viz. a constant Breeze, with that of the Arbor, Shade, or Shelter from theSun: also with that of theShadowfrom the Cloud passing under his Disk, which affected a complete Thermometer and Hygrometer.
284. On a Change of Weather from Frost to Thaw, the Colour of theupper Airfirstalters from aclear and deep, to adull and faintBlue, or to a muddy Haze, not distinguishable into Clouds, but visible above them; a vivid Brightness still remaining, for many Hours, to about 500 Yards above the Surface of the Earth.
Or, softwarmShowers fall gently, without Wind, or any apparent Change in its Direction.
All which seem to favour the Accumulation and Descent ofwarm Air, by Waves of the Apogay rolling over the Eknèfiai Winds.