CHAPTERXXXXVI.Section 254.THE Subject ofdepressing torrentsrequires an accurateInvestigation: as it will serve to point out the proper Time of Day or Night, when an Aironaut ought so to calculate his Voyage, as to arrive over the Middle of the Channel, or Arm of the Sea, at some particular Hour: in order to wait for a Sea Breeze which may waft him to the other Side.A Point not difficult to be ascertained.Also, this Idea ofdepression, if properly considered and digested; may prove a sufficient Foundation on which to establish a new Theory of theWeather, so ill determined at present, from itsaggregate WeightorElasticityonly, as indicated by the Barometer.255. If a Conjecture may be formed on a Subject, material in itself, yet of which so little is actually known; woud notthe proper Timeof undertaking a Voyage over the Channel be such, that the Aironaut shoud find himself three Parts of the Way across, bynineo’Clockin the Morning?256. InwarmerClimates, where the Seasons are more regular; theLand-Breezeblows to Sea from Midnight till X. in the Morning: at which Time, theSea-Breezeblows to Land; continues till V. or VI. in the Evening; and is succeeded by acalm, which lasts till Midnight.Whence it follows, that during the Time of the Sea-Breeze, there is a constant Tendency towards agulph of air,along the Middleof the Channel: the Equilibrium of which is as constantly supplied by aDepressionof the upper and in general cooler Strata of Air; and therefore adangerousTime for the Passage of Balloons.On the contrary, during the Night, and till ten in the Morning, there is anAccumulationof Air,along the Middle of the Channel: which consequently is a proper Time to ensure asafePassage; by the Assistance ofwings, or somepropulsiveMachinery.Of the horizontally calm mediocèanal depressing Current.257. The Deficiency or Vacuity being supplied from the etherial Regions; it might be taken for granted, that such Ether must beconsiderablylighter than the adjacent common Air on an equal Level, and thereforeproportionablydangerous for the Passage of Balloons.But if it be considered that such Air, acting as awedge, or more probably in the Form of an hyperbòlic Solid,[68]to fill up the Vacuity, descends with Rapidity from acolderAtmosphere impregnated with aqueous Vapoursinvisible from below; and that both the Air and Vapour have reciprocal Affinities and Attractions, electric and mechanical, with the Body of Water beneath them; and are often rendered still cooler by its constant Agitation andEvaporation; also, that the Supply being immediate and cotemporary, with thedouble tide of airflowing from themiddleover theoppositeShores;—there possibly may be little or no Difference between the aggregate orbarometricGravity ofsuchColumns, and those which are formed by the Sea-Breeze on either Side of them: therefore the Descent of Balloonsis owing, among other Causes, to an almost perpendicular actual Depression of the superincumbent Atmosphere.[69]Following up the Idea of a Sea-Breeze, blowing, at a Medium, for 20 Miles over Land; altho’ the Stratum of thelower currentof Air, or Sea Breeze, may not exceedhalf a mile in depth, measuring from the Ground upwards; nearly equal to 26 Inches of the Barometerabove, the Thermometer alsoabovebeing at 55, i. e.Temperate:—yet this Observation may prove of essential Service, while theupper currentof Air, i. e. the general Wind blowstowardsthe Sea, (which will be found to take Place morefrequentlythan is, at present, imagined;) or while the Balloon is influenced that Way; as was the Case with Sadler and his Companion when over the Nore: who, on his accidental and sudden Descent, fortunately found Safety in thesea-breeze.Which Breeze was sought for, and made Use of by the Author, when in the Balloon, near Frodsham, in Cheshire.For, as the Sea-Breeze is pretty general, Aironauts shoud not be too apprehensive: as they have it in their Power, by proper Management, to drop into the Breeze—foreither shore: if they are provided with a Machinery to waft themselves across the intermediatedepressingoraccumulatingmediocèanal column of air:which Space, between the two Shores, is, as before hinted, frequentlybecalmed.258. Further: as the above Theory of amediocèanalDepression seems to receive additional Confirmation fromeachBalloon Experiment; Lunardidescendingon the 5th of October last, when near the Middle of the Bay of Edinburgh or Firth of Forth;—it may be foundprudent, to keep the Balloon continually rising, till the Aironaut isone-thirdof the Passageover.258. 2. For if the general Wind in the upper Current be not strong; the Aironaut may expect to bebecalmed, with Respect to the horizontal Direction of the Current, the Instant he finds, by the Rise of the Barometer, that the Balloondescends; i. e. when it is acted upon by the depressing Column: in which Case, thehigherhe has soared, thesafer: as he will have more Room and greaterLatitudefor Exertion by Means of the Machinery: which Machinery will be greatlyaidedby the Force of the descending Column or Gravity; and will act on a similar Principle with the Ferry-Boats over the River Po in Italy; which are a Sort of horizontal Pendulum. For the Aironauts will continue todescend, at the same Time that theirWingsfurnish the Means of a progressive Motion.Therefore, before the Time that the Balloon has reached the Surface of the Water; they will have crossed the depressing Column; and find themselves waftedgentlyby thenewSea-Breeze setting in towards the opposite Shore.259. If the Aironautrises upto Sea with a Wind blowing from the Land on each of the oppositeSides of the Channel, and arrives above the Middle of the Channel, while the same Wind remains; it is probable that the Balloon will continue to rise higher as he proceeds towards the Middle,wherethemediocèanal accumulationhas for some Hours taken Place; and therefore he need not be under any Apprehension of falling: but, as before, it being probable he will also bebecalmed; the Necessity of propulsive Machinery is equally urgent, in order to pass the Center of theAccumulation: after which, the Balloon will ride Home to the opposite Shore in the new Sea-Breeze, bythatTime, just beginning to set in.260. With the Assistance of propulsive Machinery, it is imagined the Aironaut may be enabled in a few Minutes to force throu’ the calm mediocèanal Accumulation, or Depression: after which, he will have little Occasion to make Use of it.261.Sunriseis, probably, thesafestTime of all, to ascend towards the Sea, with anAir-tightBalloon: arriving with the Assistance of the Wings, throu’ thecalmmediocèanal Accumulation: and there waiting till the newSea-Breezesets in to theoppositeShore.
CHAPTERXXXXVI.
Section 254.THE Subject ofdepressing torrentsrequires an accurateInvestigation: as it will serve to point out the proper Time of Day or Night, when an Aironaut ought so to calculate his Voyage, as to arrive over the Middle of the Channel, or Arm of the Sea, at some particular Hour: in order to wait for a Sea Breeze which may waft him to the other Side.
A Point not difficult to be ascertained.
Also, this Idea ofdepression, if properly considered and digested; may prove a sufficient Foundation on which to establish a new Theory of theWeather, so ill determined at present, from itsaggregate WeightorElasticityonly, as indicated by the Barometer.
255. If a Conjecture may be formed on a Subject, material in itself, yet of which so little is actually known; woud notthe proper Timeof undertaking a Voyage over the Channel be such, that the Aironaut shoud find himself three Parts of the Way across, bynineo’Clockin the Morning?
256. InwarmerClimates, where the Seasons are more regular; theLand-Breezeblows to Sea from Midnight till X. in the Morning: at which Time, theSea-Breezeblows to Land; continues till V. or VI. in the Evening; and is succeeded by acalm, which lasts till Midnight.
Whence it follows, that during the Time of the Sea-Breeze, there is a constant Tendency towards agulph of air,along the Middleof the Channel: the Equilibrium of which is as constantly supplied by aDepressionof the upper and in general cooler Strata of Air; and therefore adangerousTime for the Passage of Balloons.
On the contrary, during the Night, and till ten in the Morning, there is anAccumulationof Air,along the Middle of the Channel: which consequently is a proper Time to ensure asafePassage; by the Assistance ofwings, or somepropulsiveMachinery.
Of the horizontally calm mediocèanal depressing Current.
257. The Deficiency or Vacuity being supplied from the etherial Regions; it might be taken for granted, that such Ether must beconsiderablylighter than the adjacent common Air on an equal Level, and thereforeproportionablydangerous for the Passage of Balloons.
But if it be considered that such Air, acting as awedge, or more probably in the Form of an hyperbòlic Solid,[68]to fill up the Vacuity, descends with Rapidity from acolderAtmosphere impregnated with aqueous Vapoursinvisible from below; and that both the Air and Vapour have reciprocal Affinities and Attractions, electric and mechanical, with the Body of Water beneath them; and are often rendered still cooler by its constant Agitation andEvaporation; also, that the Supply being immediate and cotemporary, with thedouble tide of airflowing from themiddleover theoppositeShores;—there possibly may be little or no Difference between the aggregate orbarometricGravity ofsuchColumns, and those which are formed by the Sea-Breeze on either Side of them: therefore the Descent of Balloonsis owing, among other Causes, to an almost perpendicular actual Depression of the superincumbent Atmosphere.[69]
Following up the Idea of a Sea-Breeze, blowing, at a Medium, for 20 Miles over Land; altho’ the Stratum of thelower currentof Air, or Sea Breeze, may not exceedhalf a mile in depth, measuring from the Ground upwards; nearly equal to 26 Inches of the Barometerabove, the Thermometer alsoabovebeing at 55, i. e.Temperate:—yet this Observation may prove of essential Service, while theupper currentof Air, i. e. the general Wind blowstowardsthe Sea, (which will be found to take Place morefrequentlythan is, at present, imagined;) or while the Balloon is influenced that Way; as was the Case with Sadler and his Companion when over the Nore: who, on his accidental and sudden Descent, fortunately found Safety in thesea-breeze.
Which Breeze was sought for, and made Use of by the Author, when in the Balloon, near Frodsham, in Cheshire.
For, as the Sea-Breeze is pretty general, Aironauts shoud not be too apprehensive: as they have it in their Power, by proper Management, to drop into the Breeze—foreither shore: if they are provided with a Machinery to waft themselves across the intermediatedepressingoraccumulatingmediocèanal column of air:which Space, between the two Shores, is, as before hinted, frequentlybecalmed.
258. Further: as the above Theory of amediocèanalDepression seems to receive additional Confirmation fromeachBalloon Experiment; Lunardidescendingon the 5th of October last, when near the Middle of the Bay of Edinburgh or Firth of Forth;—it may be foundprudent, to keep the Balloon continually rising, till the Aironaut isone-thirdof the Passageover.
258. 2. For if the general Wind in the upper Current be not strong; the Aironaut may expect to bebecalmed, with Respect to the horizontal Direction of the Current, the Instant he finds, by the Rise of the Barometer, that the Balloondescends; i. e. when it is acted upon by the depressing Column: in which Case, thehigherhe has soared, thesafer: as he will have more Room and greaterLatitudefor Exertion by Means of the Machinery: which Machinery will be greatlyaidedby the Force of the descending Column or Gravity; and will act on a similar Principle with the Ferry-Boats over the River Po in Italy; which are a Sort of horizontal Pendulum. For the Aironauts will continue todescend, at the same Time that theirWingsfurnish the Means of a progressive Motion.
Therefore, before the Time that the Balloon has reached the Surface of the Water; they will have crossed the depressing Column; and find themselves waftedgentlyby thenewSea-Breeze setting in towards the opposite Shore.
259. If the Aironautrises upto Sea with a Wind blowing from the Land on each of the oppositeSides of the Channel, and arrives above the Middle of the Channel, while the same Wind remains; it is probable that the Balloon will continue to rise higher as he proceeds towards the Middle,wherethemediocèanal accumulationhas for some Hours taken Place; and therefore he need not be under any Apprehension of falling: but, as before, it being probable he will also bebecalmed; the Necessity of propulsive Machinery is equally urgent, in order to pass the Center of theAccumulation: after which, the Balloon will ride Home to the opposite Shore in the new Sea-Breeze, bythatTime, just beginning to set in.
260. With the Assistance of propulsive Machinery, it is imagined the Aironaut may be enabled in a few Minutes to force throu’ the calm mediocèanal Accumulation, or Depression: after which, he will have little Occasion to make Use of it.
261.Sunriseis, probably, thesafestTime of all, to ascend towards the Sea, with anAir-tightBalloon: arriving with the Assistance of the Wings, throu’ thecalmmediocèanal Accumulation: and there waiting till the newSea-Breezesets in to theoppositeShore.